1. 宾语从句：其前一定是一个及物动词或介词；
2. 定语从句：其前一定是一个名词,或用逗号隔开的一个句子.
3. 状语从句：其前一定是一个不及物动词,或一个句子.举几个例子 谢谢1. He asked where I came from. (asked 是及物动词）Your success depends on you work hard. （on 是介词）2. This is the dictionary that / which I bought yesterday. (dictionary 是个名词） He is always boasting too much, which we don't like. (逗号隔开的一个句子）3. I put the book where it used to be.(where 从句前是一个句子）