比较状语从句(Degrees of Comparison)
比较状语从句是表示比较、比例、类比等的句子。其主要句子结构如下：
a. 主语 + 谓语 + as + 形容词 / 副词 + as + 被比对象
这个句型叫等比句结构，表示两个人和事物在性质、特征等方面相似或相等，即相等的比较。 被比对象可能是从句中的主语，也可能是宾语或其他成分。两个as，作用不同，前一个as是副词，在主句中说明所比较内容的程度，后一个as是连词，含有“比”、“如同”的意思，它所引导的从句通常是省略形式。
Physics is as important as mathematics (is).
You seem to know music as well as you know astronomy.
Take as much as you want.
Is it as difficult as they say it is?
We have accomplished as much in the past three years as would have taken ten years in the past.
表示两个人或事物在性质、特征等方面的不相似或不相同时， 就用“主语 + 谓语 + not so / as +形容词 / 副词 + (名词) + as + 被比对象”这个句型。
You are not so old as you look.
There was no garden so lovely as his in this city.
It isn’t as cold as it was yesterday.
No person is either so happy or so unhappy as he imagines.
Finally he has made as much money as he wanted.
有时as看起来像是从句的主语，其实是从句的主语省略了。
There were not so many tickets available as were asked for.
You seemed to understand human nature as well as do science.
比较句的肯定形式还有the same as, such… as；否定形式还有not the same as, not such… as。
Your name is the same as your father’s.
Her dress was the same color as mine.
Your watch is not the same as his.
I never met such a man as your younger brother.
b. 主语 + 谓语 + 形容词 / 副词比较级 + than + 被比对象
在这种结构中，than是个连词，引导比较状语从句，如果被比较的对象为名词或代词，一般采用省略形式，省去与主句中相同的部分。
This river is longer than that one.
Lesson One is more interesting than Lesson Two.
He drives faster and more dangerously than you.
This test is less simple than I expected it to be.
Light does not travel at the same speed through all materials; it goes slower through some than through others.
有时，连词than后直接跟从句的谓语，这时我们可以把它看成是省略了某些词语
There were more casualties than was reported. (= than it was reported there were)
She played the piano much better than could have been expected
在这种结构中，有时比较对象需要根据上下文内容进行判断；有时对象含蓄在主句中，这时后面往往是一个表示时间或条件的修饰语。
Taking this medicine helps to relieve his headache, and makes him less ill- tempered than before.
The effects of temperature variations in integrated circuits are more uniform than if separate components are used.
than引导的从句有时可放句
首。
Than he no one could show a friendlier attitude to you.
在一定上下文中，从句还可以省略。
You ought to come here earlier.
c. 主语 + 谓语 + 形容词 / 副词最高级 +（名词）+ 范围
在这个句子结构中，形容词最高级的前面要加定冠词the。副词最高级的前面可加the可不加。形容词最高级后面可跟名词，而副词后面却不能跟名词，它只能修饰动词。比较范围一般是短语或从句。
This coat is the most expensive that I’ve ever bought.
She is the most active girl in our class.
He worked hardest in the workshop.
She bought the least expensive towels that she could find.
最高级还可以用下列结构表示：
①… 否定词语… + 比较级…
I have never seen a taller building.
No other book has had a greater influence on my life
②… 否定词语… + so + 形容词 / 副词 + as + 比较对象
There is nothing I like so much as traveling abroad.
He has never been so happy as he is today.
③more… than any other…
She is more beautiful than any other girl in the school.
This teacher explained the problem more clearly than any other teacher.
④as… as any…
He runs as fast as any other student in the class.
This river is as long as any other in the world.
d. the + 比较级，the + 比较级
这是表示比例的句型，意思是“越…，就越…”。后面跟的是形容词或副词的比较级。通常，前面为条件从句，后面为结果主句。
The more tickets you sell, the more money you will get.
The smaller the computer is, the faster it can work.
The more he thought, the angrier he grew.
有时主句在前，从句在后：
An object draws the harder, the more matter it contains. (物体含有的物质越多，它的引力就越大。)
Others will suspect us the more, the more we suspect them.
这种句型常用省略句。
The more, the better.
The sooner, the worse.
The smaller the mind, the greater the conceit.
主句的主谓有时半倒装，以保持句子的平衡。
The more you read, the better will you write.
The smaller the particles(分子) are, the more freely do they move.
e. 类比句，表示两类事物的相同或相似关系，通常用连词或引导从句。其主要句型结构有：
1.A is to B what/as C is to D.
Reading is to the mind what exercise is to the body.
Manure is to crops as food is to man
2.A does for B what C does for D.
Leaves do for plants what lungs do for animals.
3.A is that to B which C is to D.
Intellect is that to the mind which sight is to the body.
4.A does that for B which C does for D.
Railways do that for a country which blood vessels do for a man’s body.