As能引导几种从句：
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。as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.