1.基本用法
该结构的基本意思是“与……一样”，其中接形容词或副词的原级，在否定句中，第一个as也可换成so.如：
He doesn't study as [so] hard as his brother. 他学习不如他弟弟努力。
2.涉及数量或程度的用法
若涉及数量或程度，可用“as much+不可数名词+as”和“asmany+可数名词复数+as”。如：
He doesn‘t pay as much tax as we do / as us. 他没我们交的税款多。
There are not as many restaurants as there were. 现在餐馆没有过去多了。
3.有关词序的一点说明
其间接形容词时，有时该形容词还可修饰另一名词，但这个名词应带有不定冠词(注意词序)。如：
I have as good a voice as you. 我的声音和你一样好。
4.该结构的修饰语
根据情况可用(not) nearly, almost, just, nothing like, exactly, not quite, half, one-ten, twice, threetimes, 30 per cent等修饰，并且这些修饰语必须置于第一个as之前，而不能置于其后。如：
This room is twice as large as that one. 这个房间是那个房间的两个大。
You‘re not half as clever us you think you are. 你远不是自己想像的那么聪明。
It took three times as long as I had expected. 这件事比我预料的多花了两倍的时间。
英语四级语法考点复习：
1、从词性上看区别
first可用作形容词或副词，有时还可用作代词;而at first作为介词短语，只起副词用作用(在句中用作状语)。如：
First class is the most expensive way to travel. 坐头等舱是最贵的旅行方式。(first为形容词，在句中用作定语)
This is the first time I have heard of such things. 这是我第一次听到这样的事。(first为形容词，在句中用作定语)
You needn‘t read the whole book hut you must readthe first four chapters.你们不必把整本书全读完，但必须读完前四章。(first为形容词，在句中用作定语)
I asked them to ring first in case we were out. 我请他们先打电话来，以防我们不在家。(first为副词，在句中用作状语)
She‘s always the first to arrive and the last to leave. 她总是第一个来，最后一个离开。(first为代词，可视为其后省略了one， person等之类的词)
His second suggestion was not much better than his first. 他的第二个建议比第一个好不了多少。(first为代词，可视为其后省略了suggestion)
At first we used hand tools. Later we had machines. 开始我们用手工工具，后来我们有了机器。(atfirst在此用作状语)
2、从用法上看区别
1).first的用法
first 用来说明顺序，意为“先……”，暗示接下去还有其他动作或事件要发生，因此其后往往接有(或暗示有)then，next，last 等词。如：
Think first, then act. 先想清楚再行动。
I‘ll have to finish my homework first. 我得先把作业做完。
First(you)boil some water. Then(you)warm the teapot. Then(you)add three teaspoons oftea. Next,(you)pour on boiling water… 你先烧些开水，然后把茶壶烫热，接着放三勺茶叶，随后冲入开水……
John came home from work. First he read the paper for a while, then he got up from the chairand turned on the radio. 约翰下班回家，先看一会儿报，然后从椅子上站起来，打开收音机。
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