加形容词或副词的原级。as的用法如下：as+形容词/副词+as；as+形容词+a+单数可数名词+as；as...as中间加形容词或副词的原级。
as...as的用法
1.as...as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.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。
3.as...as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,three times,30 percent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。
