在学习英语语法时，定语从句是一个重要的组成部分。定语从句用来修饰名词，提供关于该名词的更多信息。理解如何使用关系代词来引导定语从句，对于提高英语表达能力至关重要。关系代词如who, whom, whose, that 和 which 不仅代表前面的名词，还将从句与其修饰的词连接起来，同时在从句中担任不同的语法角色。这些关系代词的使用规则涉及到主语、宾语和介词宾语等不同情况。
<例句>
I met someone who said he knew you.
我遇到一个人，他说他认识你。
<语法分析>
关系代词 who 代表 someone，又引导从句修饰它，同时又在从句中担任主语。关系代词 who, whom, whose, that和 which可以用来引导定语从句，这类代词都起着三重作用，一是代表前面的名词，二是把从句和它所修饰的词连接起来，三是在从句里也担任一个成分。who 和 whom 都代表人，who 在从句中作主语，whom在从句中作宾语或介词宾语。whose在从句中可以作定语。that可以代表人或物，which 只能代表物在从句中可充当主语、宾语或介词宾语等。
<触类旁通>
(1) The noise that she made woke everybody up.
她弄出的声音把大家都吵醒了。
语法分析：that 代表 noise，又引导从句修饰它，在从句中担任 made 的宾语。
(2) She saw something in the paper which might interest you.
她在报纸上看到的一些消息，或许会使你感兴趣。
语法分析：which 代表 something, 又引导从句修饰它，在从句中担任主语。
(3) The girl with whom I was travlling didn't speak English.
和我一起旅行的那个女孩不会讲英语。
语法分析：whom 代表人，在从句中作宾语或介词宾语。
(4) I saw a film whose name I have forgotten.
我看了一部电影， 名字却忘了。
语法分析：whose 有时指无生命的东西。
(5) Who's the man (that) you were talking to?
刚才和你讲话的人是谁?
语法分析：在从句作宾语时，that常可以省略。
(6) The situation in which she found herself was very difficult.
她的处境非常困难。
语法分析：在紧跟介词时，只能用which，不能用that，而且不能省略。
<巩固练习>
1. The man _____ robbed her has been arrested.
2. The man _____ I saw told me to come back tomorrow.
3. I know a girl _____ mother is an acrobat.
4. He _____ would eat the fruit must climb the tree.
5. The dog _____ was lost has been found.
6. She invited us to dinner, ______ was very kind of her.
7. My dog, ______ temper is very uncertain, often bites judges at dog show.
8. The man from ______ I brought it told me to read me instructions.
<参考答案>
1. who 2. whom 3. whose 4. that 5. which 6. which 7. whose 8. whom