1、As可以引导定语从句.有时可译为“正如”.此时，常常是as从句在前，主句在后.
例如：As we can see，he is a Chinese.
2、As 还可引导原因状语从句，“因为，由于”
例如：As he is so lazy，he never cooks by himself.
3、As还可引导时间状语从句，“当，随着”
例如：As the weather is colder and colder，the leaves of the tree is less and less.
4、As还可引导方式状语从句，“按照”
例如：You must do the work as I have told you.
5、As还可引导让步状语从句.“尽管”.但是注意，as引导方式状语从句时从句必须倒装.而且这种倒装和一般的倒装不一样从句的倒装一般是把从句的表语或作状语的副词提到as之前，（如果表语是一个带有不定冠词a或an的单数名词，倒装后a或an必须省略).
例如：Though he is a little boy，he knows a lot.如果变成由AS引导，就必须变成：
Little boy as he is，he knows a lot.
Though he works hard，he never succeed.
可变为 Hard as he works，he never succeed.
