Question

定语从句中什么时候用which/ that/ who/ what

Answer 1

介词+WHICH在定语从句中可以代替when,where,和why，用哪一个介词要看先行词和从句谓语动词，介词要能够与先行词搭配使用
、"介词+关系代词"引导的定语从句

关系代词whom, which在定语从句中作介词的宾语时,可以跟介词一起放在主句和从句之间;当先行词指人时,介词后的关系代词用whom, 其余用which,这时的关系代词不能省略;有时为了使关系代词紧跟它所修饰的先行词,也可以把介词放在从句中有关动词的后面,这时的which可用that替换。当介词放在从句有关动词的后面时,关系代词which, that, whom在口语中和非正式文体中经常省略。如:

This is the room in which he used to live. = This is the room (which / that) he used to live in. 这是他过去居住过的房间。

Who's the man with whom you just shook hands? =Who's the man (that / whom) you just shook hands with? 刚才你与他握手的那个人是谁?

但含有介词的短语动词一般不拆开,介词仍放在动词的后面。如:

This is the book (which / that) I'm looking for. 这就是我在找的那本书。

在这类定语从句中,介词的选择一般根据动词的需要,如上述几例,或者根据先行词来决定。如:

There is a mountain of which the top is always covered with snow. 有一座山顶总是覆盖着雪的山。