as...as表示像...一样，（强调数量）多达，只有。通常中间只能用形容词或副词的原级，不能用比较级或最高级。若第二个as之后使用独立的人称代词，一般用主格(较正式)或宾格(非正式)均可。
1.若涉及数量或程度，可用“as much+不可数名词+as”和“as many+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。
2.“as+形容词或副词原级+as...”意为“和...一样”，表示同级的比较，第一个as为副词，第二个as为连词。
（1）as...as结构用于表示不同人或物同一性质的比较，意为...和...一样
The tree is as tall as the building.这棵树和那栋楼一样高。
（2）as...as结构用于表示同一个人或物不同性质的比较，意为既...又...
This swimming pool is as wide as it is long.
这个游泳池宽度和长度相等。
（3）as...as结构用于表示两个人或物不同性质的比较，表示程度相同或相当，意为...而...，在否定句结构是so/as...as...
He cannot run so/as fast as you.他没你跑得快。
He was as handsome as his wife was beautiful.
他长得很英俊，他的妻子也长得非常漂亮。
3.as...as的常见句型
（1）as...as possible／sb can尽可能的……
Please answer my question as soon as possible．
请尽快回答我的问题。
The detective is searching the man as carefully as he can．
那个侦探正在尽可能仔细地搜查那个男子的身体。
（2）as...as usual／before像以前一样……
She looks as pretty as before．
她看起来和以前一样漂亮
Though they failed，they still worked as hard as usual．
尽管他们失败了，但他们仍像以前一样努力工作。
（3）as long as只要，引导条件状语从句
I will stay with you as long as there is a room free．
要是你有一间空余的房子，我就住在你这里。
You may borrow this book as long as you promise to give it back
只要你答应归还，你就可以把这书借走。
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