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TPO-41 阅读文本和对应题目文本 第2篇

Climate of Venus

Earth has abundant water in its oceans but very little carbon dioxide in its relatively thin atmosphere. By contrast, Venus is very dry and its thick atmosphere is mostly carbon dioxide. The original atmospheres of both Venus and Earth were derived at least in part from gases spewed forth, or outgassed, by volcanoes. The gases that emanate from present-day volcanoes on Earth, such as Mount Saint Helens, are predominantly water vapor, carbon dioxide, and sulfur dioxide. These gases should therefore have been important parts of the original atmospheres of both Venus and Earth. Much of the water on both planets is also thought to have come from impacts from comets, icy bodies formed in the outer solar system.

In fact, water probably once dominated the Venusian atmosphere. Venus and Earth are similar in size and mass, so Venusian volcanoes may well have outgassed as much water vapor as on Earth, and both planets would have had about the same number of comets strike their surfaces. Studies of how stars evolve suggest that the early Sun was only about 70 percent as luminous as it is now, so the temperature in Venus’ early atmosphere must have been quite a bit lower. Thus water vapor would have been able to liquefy and form oceans on Venus. But if water vapor and carbon dioxide were once so common in the atmospheres of both Earth and Venus, what became of Earth’s carbon dioxide? And what happened to the water on Venus?

The answer to the first question is that carbon dioxide is still found in abundance on Earth, but now, instead of being in the form of atmospheric carbon dioxide, it is either dissolved in the oceans or chemically bound into carbonate rocks, such as the limestone and marble that formed in the oceans. If Earth became as hot as Venus, much of its carbon dioxide would be boiled out of the oceans and baked out of the crust. Our planet would soon develop a thick, oppressive carbon dioxide atmosphere much like that of Venus.

To answer the question about Venus’ lack of water, we must return to the early history of the planet. Just as on present-day Earth, the oceans of Venus limited the amount of atmospheric carbon dioxide by dissolving it in the oceans and binding it up in carbonate rocks. But being closer to the Sun than Earth is, enough of the liquid water on Venus would have vaporized to create a thick cover of water vapor clouds. Since water vapor is a greenhouse gas, this humid atmosphere—perhaps denser than Earth’s present-day atmosphere, but far less dense than the atmosphere that envelops Venus today—would have efficiently trapped heat from the Sun. At first, this would have had little effect on the oceans of Venus. Although the temperature would have climbed above 100° C, the boiling point of water at sea level on Earth, the added atmospheric pressure from water vapor would have kept the water in Venus’ oceans in the liquid state.

This hot and humid state of affairs may have persisted for several hundred million years. But as the Sun’s energy output slowly increased over time, the tempera ture at the surface would eventually have risen above 374°C. Above this temperature, no matter what the atmospheric pressure. Venus’ oceans would have begun to evaporate, and the added water vapor in the atmosphere would have increased the greenhouse effect. This would have made the temperature even higher and caused the oceans to evaporate faster, producing more water vapor. That, in turn, would have further intensified the greenhouse effect and made the temperature climb higher still.

Once Venus’ oceans d isappeared, so did the mechanism for removing carbon dioxide from the atmosphere. With no oceans to dissolve it, outgassed carbon dioxide began to accumulate in the atmosphere, intensifying the greenhouse effect even more Temperatures eventually became high

enough to" bake out” any carbon dioxide that was trapped in carbonate rocks. This liberated carbon dioxide formed the thick atmosphere of present-day Venus. Over time, the rising temperatures would have leveled off, solar ultraviolet radiation having broken down atmospheric water vapor molecules into hydrogen and oxygen. With all the water vapor gone, the greenhouse effect would no longer have accelerated.

Paragraph 1

Earth has abundant water in its oceans but very little carbon dioxide in its relatively thin atmosphere. By contrast, Venus is very dry and its thick atmosphere is mostly carbon dioxide. The original atmospheres of both Venus and Earth were derived at least in part from gases spewed forth, or outgassed, by volcanoes. The gases that emanate from present-day volcanoes on Earth, such as Mount Saint Helens, are predominantly water vapor, carbon dioxide, and sulfur dioxide. These gases should therefore have been important parts of the original atmospheres of both Venus and Earth. Much of the water on both planets is also thought to have come from impacts from comets, icy bodies formed in the outer solar system.

1. According to paragraph 1, in what major respect are Venus and Earth different from each other?

A. Whether carbon dioxide v/as present in their original atmospheres

B.How thin their original atmospheres were

C. What their present-day atmospheres mainly consist of

D. How long ago they first developed an atmosphere

2. Why does the author mention "present-day volcanoes on Earth"?

A. To provide an example of an important difference between present-day Venus and present-day Earth

B. To help explain why Earth's atmosphere still contains traces of sulfur dioxide but Venus' does not

C. To indicate one source of information about the likely composition of the original atmospheres of Venus and Earth

D. To account for the fact that Earth’s water supply no longer comes primarily from impacting comets

Paragraph 2

In fact, water probably once dominated the Venusian atmosphere. Venus and Earth are similar in size and mass, so Venusian volcanoes may well have outgassed as much water vapor as on Earth, and both planets would have had about the same number of comets strike their surfaces. Studies of how stars evolve suggest that the early Sun was only about 70 percent as luminous as it is now, so the temperature in Venus’ early atmosphere must have been quite a bit lower. Thus water vapor would have been able to liquefy and form oceans on Venus. But if water vapor and carbon dioxide were once so common in the atmospheres of both Earth and Venus, what became of Earth’s carbon dioxide? And what happened to the water on Venus?

3. According to paragraph 2, what is one reason for thinking that at one time, there were significant amounts of water on Venus?

A. B ecause of Venus’ size and mass, its volcanoes probably produced much more water vapor than

volcanoes on Earth did.

B. The low temperature of Venus' early atmosphere can be explained only by the presence of water.

C. The presence of carbon dioxide in a planet's atmosphere is an indicator of water on that planet.

D. Venus probably was struck by roughly as many comets as Earth was.

4. The word “luminous” in the passage is closest in meaning to

A. dense

B. bright

C. large

D. active

Paragraph 3

The answer to the first question is that carbon dioxide is still found in abundance on Earth, but now, instead of being in the form of atmospheric carbon dioxide, it is either dissolved in the oceans or chemically bound into carbonate rocks, such as the limestone and marble that formed in the oceans. If Earth became as hot as Venus, much of its carbon dioxide would be boiled out of the oceans and baked out of the crust. Our planet would soon develop a thick, oppressive carbon dioxide atmosphere much like that of Venus.

5. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A. The first question to be answered is how Earth’s atmospheric carbon dioxide either got dissolved in the oceans or got chemically bound into carbonate rocks.

B. The fact that Earth’s abundant carbon dioxide is more often found in carbonate rock than dissolved in the oceans is the answer to the first question.

C.Earth still has abundant carbon dioxide, but instead of being in the atmosphere it is now dissolved in the oceans or chemically bound into ocean rock s.

D. The formation of limestone and marble used up the carbon dioxide that was dissolved in Ear th’s oceans so that only carbon dioxide in atmospheric form remained.

Paragraph 4

To answer the question about Venus’ lack of water, we must return to the early history of the planet. Just as on present-day Earth, the oceans of Venus limited the amount of atmospheric carbon dioxide by dissolving it in the oceans and binding it up in carbonate rocks. But being closer to the Sun than Earth is, enough of the liquid water on Venus would have vaporized to create a thick cover of water vapor clouds. Since water vapor is a greenhouse gas, this humid atmosphere—perhaps denser than Earth’s present-day atmosphere, but far less dense than the atmosphere that envelops Venus today—would have efficiently trapped heat from the Sun. At first, this would have had little effect on the oceans of Venus. Although the temperature would have climbed above 100° C, the boiling point of water at sea level on Earth, the added atmospheric pressure from water vapor would have kept the water in Venus’ oceans in the liquid state.

6. According to paragraph 4, what is one factor that kept the amount of carbon dioxide in the

atmosphere of early Venus relatively low?

A.The presence of water vapor clouds

B.The presence of oceans

C.Rapidly increasing temperatures at ground level

D. Low atmospheric pressures

Paragraph 6

Once Venus’ oceans disappeared, so did the mechanism for removing carbon dioxide from the atmosphere. With no oceans to dissolve it, outgassed carbon dioxide began to accumulate in the atmosphere, intensifying the greenhouse effect even more Temperatures eventually became high enough to" bake out” any carbon dioxide that was trapped in carbonate rocks. This liberated carbon dioxide formed the thick atmosphere of present-day Venus. Over time, the rising temperatures would have leveled off, solar ultraviolet radiation having broken down atmospheric water vapor molecules into hydrogen and oxygen. With all the water vapor gone, the greenhouse effect would no longer have accelerated.

7. The phrase “mechanism for” in the passage is c losest in meaning to

A. means of

B. importance of

C. need for

D. benefits of

Paragraph 5

This hot and humid state of affairs may have persisted for several hundred million years. But as the Sun’s energy output slowly increased over time, the temperature a t the surface would eventually have risen above 374°C. Above this temperature, no matter what the atmospheric pressure. Venus’ oceans would have begun to evaporate, and the added water vapor in the atmosphere would have increased the greenhouse effect. This would have made the temperature even higher and caused the oceans to evaporate faster, producing more water vapor. That, in turn, would have further intensified the greenhouse effect and made the temperature climb higher still.

8. The word “persisted” i n the passage is closest in meaning to

A. improved

B. continued

C. weakened

D. evolved

9. According to paragraph 5, what happens when temperatures rise above 374°C?

A. Atmospheric pressure begins to decrease.

B. Water vapor disappears from the atmosphere.

C. Water evaporates regardless of atmospheric pressure.

D. More energy is required to evaporate a given volume of water.

Paragraph 6

Once Venus’ oceans disappeared, so did the mechanism for removing carbon dioxide from the atmosphere. With no oceans to dissolve it, outgassed carbon dioxide began to accumulate in the atmosphere, intensifying the greenhouse effect even more Temperatures eventually became high enough to" bake out” any carbon dioxide that was trapped in carbonate rocks. This liberated carb on dioxide formed the thick atmosphere of present-day Venus. Over time, the rising temperatures would have leveled off, solar ultraviolet radiation having broken down atmospheric water vapor molecules into hydrogen and oxygen. With all the water vapor gone, the greenhouse effect would no longer have accelerated.

10. According to paragraph 6, extremely high temperatures increased the amount of carbon dioxide in Venus’ atmosphere by

A. increasing the rate which carbon dioxide was outgassed

B. baking out carbon dioxide from carbonate rocks

C. creating additional water vapor

D. replacing the previous mechanisms for removing carbon dioxide with less effective ones

11. The passage supports the idea that the basic reason that Venus and Earth are now so different from each other is that

A.early Venus had more frequent volcanic outgassing than early Earth did

B. early Venus had far less liquid water than early Earth did

C. volcanic activity stopped relatively early on Venus but continued on Earth

D.Venus is closer to the Sun than Earth is

Paragraph 5

12. Look at the four squares [■] that indicate where the following sentence could be added to the passage.

This cycle of rising temperatures following an increase in greenhouse gases is known as the

runaway greenhouse effect.

Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.

This hot and humid state of affairs may have persisted for several hundred million years. But as the Sun’s energy output slowly increased over time, the temperature at the surface would eventually have risen above 374°C.[■] Above this temperature, no matter what the atmospheric pressure. Venus’ oceans would have begun to evaporate, and the added water vapor in the atmosphere would have increased the greenhouse effect.[■] This would have made the temperature even higher and caused the oceans to evaporate faster, producing more water vapor. [■] That, in turn, would have further intensified the greenhouse effect and made the temperature climb higher still.[■]

13. Directions: Select from the seven phrases below the 2 phrases that correctly characterize early

Venus and the 3 phrases that correctly characterize present-day Venus. Drag each phrase you select into the appropriate column of the table. Two of the phrases will NOT be used. This question is worth 3 points.

Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it.

To review the passage, click VIEW TEXT.

Early Venus

Present-day Venus

Answer Choices

A.High percentage of water vapor in the atmosphere

B.Carbon dioxide present only in atmospheric form

C.An atmosphere quite similar to that of early Earth

D.Very dense but relatively cool atmosphere

http://www.wendangku.net/doc/2aea5bdf5f0e7cd1852536c6.htmlpletely covered with water

http://www.wendangku.net/doc/2aea5bdf5f0e7cd1852536c6.htmlplete absence of surface water

G. Essentially stable temperatures

Amphibian Thermoregulation

In contrast to mammals and birds, amphibians are unable to produce thermal energy through their metabolic activity, which would allow them to regulate their body temperature independent of the surrounding or ambient temperature. However, the idea that amphibians have no control whatsoever over their body temperature has been proven false because their body temperature does not always correspond to the surrounding temperature. While amphibians are poor thermoregulators, they do exercise control over their body temperature to a limited degree.

Physiological adaptations can assist amphibians in colonizing habitats where extreme conditions prevail. The tolerance range in body temperature represents the range of temperatures within which a species can survive. One species of North American newt is still active when temperatures drop to -2°C while one South American frog feels comfortable even when temperatures rise to 41°C—the highest body temperature measured in a free-ranging amphibian. Recently it has been shown that some North American frog and toad species can survive up to five days with a body temperature of -6°C with approximately one-third of their body fluids frozen. The other tissues are protected because they contain the frost-protective agents glycerin or glucose Additionally, in many species the tolerance boundaries are flexible and can change as a result of acclimatization (long-term exposure to particular conditions).

Frog species that remain exposed to the sun despite high diurnal (daytime) temperatures exhibit some fascinating modifications in the skin structure that function as morphological adaptations. Most amphibian skin is fully water permeable and is therefore not a barrier against evaporation or solar radiation. The African savanna frog Hyperolius viridiflavus stores guanine crystals in its skin, which enable it to better reflect solar radiation, thus providing protection against overheating. The tree frog Phyllomedusa sauvagei responds to evaporative losses with gland secretions that provide a greasy film over its entire body that helps prevent desiccation (dehydration).

However, behavior is by far the most important factor in thermoregulation. The principal elements in behavioral thermoregulation are basking (heliothermy), heat exchange with substrates such as rock or earth (thigmothermy), and diurnal and annual avoidance behaviors, which include moving to shelter during the day for cooling and hibernating or estivating (reducing activity during cold or hot weather, respectively) Heliothermy is especially common among frogs and toads: it allows them to increase their body temperature by more than 10°C. The Andean toad Bufo spinulosus exposes itself immediately after sunrise on moist ground and attains its preferred body temperature by this means, long before either ground or air is correspondingly warmed. A positive side effect of this approach is that it accelerates the digestion of the prey consumed overnight, thus also accelerating growth. Thigmothermy is a behavior present in most amphibians, although pressing against the ground serves a dual purpose: heat absorption by conductivity and water absorption through the skin. The effect of thigmothermy is especially evident in the Andean toad during rainfall: its body temperature corresponds to the temperature of the warm earth and not to the much cooler air temperature.

Avoidance behavior occurs whenever physiological and morphological adaptations are insufficient to maintain body temperature within the vital range. Nocturnal activity in amphibians with low tolerance for high ambient temperatures is a typical thermoregulatory behavior of avoidance. Seasonal avoidance behavior is extremely important in many amphibians. Species

whose habitat lies in the temperate latitudes are confronted by lethal low temperatures in winter, while species dwelling in semi- and regions are exposed to long dry, hot periods in summer.

In amphibians hibernation occurs in mud or deep holes away from frost. North of the Pyrenees Mountains, the natterjack toad offers a good example of hibernation, passing the winter dug deep into sandy ground. Conversely, natterjacks in southern Spain remain active during the mild winters common to the region and are instead forced into inactivity during the dry, hot summer season. Summer estivation also occurs by burrowing into the ground or hiding in cool, deep rock crevasses to avoid desiccation and lethal ambient temperature. Amphibians are therefore hardly at mercy of ambient temperature, since by means of the mechanisms described above they are more than )exercise some control over their body temperature.

paragraph 1

In contrast to mammals and birds, amphibians are unable to produce thermal energy through their metabolic activity, which would allow them to regulate their body temperature independent of the surrounding or ambient temperature. However, the idea that amphibians have no control whatsoever over their body temperature has been proven false because their body temperature does not always correspond to the surrounding temperature While amphibians are poor thermoregulators, they do exercise control over their body temperature to a limited degree.

1.According to paragraph 1, what indicates that amphibians have some control over their body temperature?

A. Amphibians can regulate their metabolic rates to generate energy.

B. Amphibians use the same means of thermoregulation as mammals and birds do.

C. The body temperature of amphibians sometimes differs from the temperature of their surroundings.

D. The body temperature of amphibians is independent of their metabolic activity.

paragraph 2

Physiological adaptations can assist amphibians in colonizing habitats where extreme conditions prevail. The tolerance range in body temperature represents the range of temperatures within which a species can survive. One species of North American newt is still active when temperatures drop to -2°C while one South American frog feels comfortable even when temperatures rise to 41°C—the highest body temperature measured in a free-ranging amphibian Recently it has been shown that some North American frog and toad species can survive up to five days with a body temperature of -6°C with approximately one-third of their body fluids frozen. The other tissues are protected because they contain the frost-protective agents glycerin or glucose Additionally, in many species the tolerance boundaries are flexible and can change as a result of acclimatization (long-term exposure to particular conditions)

2.Why does the author mention a “South American frog” species in the passage?

A. To make the point that an amphibian’s temperature tolerance depends on a number of factors

B. To indicate how precise the range of body temperatures is for certain amphibians

C. To contrast its ability to adapt to that of the North American newt

D. To help illustrate the range of environmental conditions to which amphibians have adapted

3. According to paragraph 2, what allows some North American frog and toad species to survive in ambient temperatures well below freezing?

A. Their internal body temperatures never fall below -6°C.

B. They do not remain at temperatures below freezing for very long periods of time.

C. Their tolerance boundaries are flexible

D. Some of their body tissues contain substances that prevent freezing.

paragraph 3

Frog species that remain exposed to the sun despite high diurnal (daytime) temperatures exhibit some fascinating modifications in the skin structure that function as morphological adaptations. Most amphibian skin is fully water permeable and is therefore not a barrier against evaporation or solar radiation. The African savanna frog Hyperolius viridiflavus stores guanine crystals in its skin, which enable it to better reflect solar radiation, thus providing protection against overheating The tree frog Phyllomedusa sauvagei responds to evaporative losses with gland secretions that provide a greasy film over its entire body that helps prevent desiccation (dehydration).

4. “Phyllomedusa sauvager ” is mentioned as an example of a frog with an adaptation that

A. protects its glandular system

B. helps reduce its secretions

C. increases the amount of solar radiation that its skin can reflect

D. modifies its skin structure to protect against the drying effects of the sun

paragraph 4

However, behavior is by far the most important factor in thermoregulation. The principal elements in behavioral thermoregulation are basking (heliothermy), heat exchange with substrates such as rock or earth (thigmothermy), and diurnal and annual avoidance behaviors, which include moving to shelter during the day for cooling and hibernating or estivating (reducing activity during cold or hot weather, respectively) Heliothermy is especially common among frogs and toads: it allows them to increase their body temperature by more than 10°C. The Andean toad Bufo spinulosus exposes itself immediately after sunrise on moist ground and attains its preferred body temperature by this means, long before either ground or air is correspondingly warmed. A positive side effect of this approach is that it accelerates the digestion of the prey consumed overnight, thus also accelerating growth Thigmothermy is a behavior present in most amphibians, although pressing against the ground serves a dual purpose heat absorption by conductivity and water absorption through the skin The effect of thigmothermy is especially evident in the Andean toad during rainfall its body temperature corresponds to the temperature of the warm earth and not to the much cooler air temperature.

5. Paragraph 4 mentions each of the following as an example of behavioral thermoregulation EXCEPT

A. pressing against the ground

B. speeding up of the metabolism

C. reducing activity during the summer

D. adjusting exposure to the sun

6. The “Andean toad Bufo spinulosus”illustrates which of the following behavioral modifications?

A. Heliothermy and thigmothermy

B. Diurnal avoidance behavior

C. Absorbing heat from the air

D. Moving to shelter during the summer

7. The word “attains” in the passage is closest in meaning to

A. raises

B. lowers

C. reaches

D. regulates

8.The phrase “this approach” in the passage refers to

A gradually increasing body temperature by 10°C

B. basking as soon as the sun comes up

C. waiting for the ground and air to warm

D. keeping body temperature above the temperature of the air

paragraph 5

Avoidance behavior occurs whenever physiological and morphological adaptations are insufficient to maintain body temperature within the vital range Nocturnal activity in amphibians with low tolerance for high ambient temperatures is a typical thermoregulatory behavior of avoidance. Seasonal avoidance behavior is extremely important in many amphibians. Species whose habitat lies in the temperate latitudes are confronted by lethal low temperatures in winter, while species dwelling in semi- and regions are exposed to long dry, hot periods in summer.

9. According to paragraph 5, why is avoidance behavior important for some amphibians?

A. Amphibians’ habitats are areas where temperatures vary from day to day.

B. Amphibians have less tolerance for high ambient temperatures than for low ambient temperatures.

C. Amphibians lack adequate physiological adaptations for dealing with ambient temperatures.

D. Amphibians cannot protect themselves from the extreme summer heat by being active only at night.

10.The word “dwelling” in the passage is closest in meaning to

A.arriving

B.originating

C.evolving

D. living

paragraph 6

In amphibians hibernation occurs in mud or deep holes away from frost North of the Pyrenees Mountains, the natterjack toad offers a good example of hibernation, passing the winter dug deep into sandy ground. Conversely, natterjacks in southern Spain remain active during the mild winters common to the region and are instead forced into inactivity during the dry, hot summer season. Summer estivation also occurs by burrowing into the ground or hiding in cool, deep rock crevasses to avoid desiccation and lethal ambient temperature. Amphibians are therefore hardly at mercy of ambient temperature, since by means of the mechanisms described above they are more than exercise some control over their body temperature.

11. In paragraph 6, which of the following can be inferred from the discussion of the natterjack?

A. Amphibians have greater tolerance for heat than for cold.

B. Desiccation is not a threat to amphibians

C. Both hibernation and estivation may serve as avoidance behaviors depending on the climate

D. Some species of amphibians are active only in the spring and in the fall

12. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A. Thus, although amphibians use the various mechanisms described above, they have hardly any control of their body temperature

B. Thus, by the mechanisms described above, amphibians are quite capable of controlling their body temperature to survive extreme ambient temperatures.

C. Thus, unless they can use the mechanisms described above, amphibians are at the mercy of ambient temperatures.

D. Thus, the mechanisms described above give amphibians control over much more than just their body temperature

13. Look at the fou r squares [■] that indicate where the following sentence could be added to the passage.

On the other hand, amphibians in very hot climates use secretions from the mucus glands to decrease their temperature through evaporative cooling on the skin.

Where would the sentence best fit? Click on square [■] to add the sentence to the passage.

Physiological adaptations can assist amphibians in colonizing habitats where extreme conditions prevail. The tolerance range in body temperature represents the range of temperatures within which a species can survive. One species of North American newt is still active when temperatures drop to -2°C while one South American frog feels comfortable even when temperatures measured to 41°C—the highest body temperature measured in a free-ranging amphibian. [■] Recently it has been shown that some North American frog and toad species can survive up to five days with a body temperature of -6°C with approximately one-third of their body fluids frozen. [■] The other tissues are protected because they contain the frost-protective agents glycerin or glucose. [■] Additionally, in many species the tolerance boundaries are flexible

and can change as a result of acclimatization (long-term exposure to particular conditions).[■]

14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selected THREE answer choices that express the most important ideas in the passage.Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth 2 points.

Drag your choices to the spaces where they belong. To review the passage, click on View Text.

A number of factors may help account for the difference in biodiversity between low and high latitudes.

Answer Choices

A. Frogs, which survive temperature ranges from as low as -2°C to as high as 41°C, are evidence that amphibians are independent of ambient temperatures

B. Amphibians can increase their body temperature by exposing themselves to the sun (heliothermy) and by pressing against the ground (thigmothermy).

C. Avoidance behaviors, such as sheltering from the sun, as well as estivation and hibernation,help amphibians control their body temperature.

D. Physical adaptations offer amphibians a number of ways to protect against extreme or dangerous climate conditions.

E. Sunrise is the time when some amphibian species have the greatest need for thermoregulatory mechanisms.

F. Hibernation always involves digging deep holes in mud or sand, whereas estivation sometimes involves nothing more than hiding in deep rock crevasses