由“介詞+關係代詞”引導的定語從句

1. 由“介詞+關係代詞”引導的定語從句主要用於正式文體，在非正式文體中通常將介詞放至句末。如：This is the man to whom I referred. 我指的就是這個人。This is the man (whom) I referred to. 我指的就是這個人。

2. 直接用於介詞後作賓語的關係代詞which不能換成that，直接用於介詞後作賓語的關係代詞whom不能換成who。但若介詞用於句末，則用作賓語的which, whom也可換成that, who，或者省略不同。如：這是一個我們討論了許多的問題。This is a subject about which we have talked a lot.(which不能換成that，也不能省略)This is a subject which we have talked about a lot. 這是一個我們討論了許多的問題。(which可以換成that，也可以省略) 

3. 關係副詞when, where, why根據情況有時可換成“介詞+關係代詞which”。如： That is the day when [=on which] he was born. 那就是他出生的日子。That is the house where [=in which] he lived. 那就是他住過的房子。That is the reason why [=for which] he must apologize. 那就是他必須道歉的原因。

4. 在很正式的文體中，“介詞+關係代詞”引導的定語從句可緊縮成“介詞+關係代詞+不定式”結構。如：在那兒孩子們有個玩耍的花園。正：There the children had a garden in which to play. (很正式)正：There the children had a garden in which they could play. (較正式)正：There the children had a garden to play in. (較口語化)注：這類“介詞+關係代詞++不定式”結構中的介詞不能沒有，也不能放在句末。如不能說There the children had a garden which to play in.