【关系代词的用法】

一般情况下，that既可指人又可指物，可以代替who, whom和which，在从句中作主语或谓语动词的宾语，但不能作介词的宾语；which指物，在从句中作主语或谓语动词的宾语；who在从句中作主语；whom在从句中作宾语；whose在从句中作定语。
如：A doctor is a_person who looks_after people's_health.
                               先行词  主语___谓语______宾语
　
who是关系代词，在定语从句中作主语。
句意：医生就是照顾人们健康的人。
I like music that I can dance to.
我喜欢我能跟着跳舞的音乐。
I love singers who write their own music.
我喜欢那些自己写歌的歌手。
Someone who is guilty has done something against the law.
犯罪的人就是做了一些违反法律的事的人。
There is a boy in our team whose parents want him to go to a sports school.
在我们小组里有一个男孩，他父母想让他进体校。

 1. 在下列情况下，只能用that引导，不能用who或which引导。
(1) 当先行词是all, little, much, none, everything, anything, nothing等代词时。
如：Is there anything that you don't understand?
你还有不懂的地方吗？
Tom told his mother all that had happened.
Tom把事情发生的全部情况告诉了他妈妈。
(2) 当先行词前面有the only, the very, the last等修饰时。
如：He is the only person that can help you out.
他是唯一一个能帮你摆脱困境的人。
(3) 当序数词或形容词最高级修饰先行词时。
如：This is the best book that I have ever read.
这是我读过的最好的书。
 (4) 当先行词前面有only, all, any, no等修饰时。
如：I want to read all the books that were written by Lu Xun.
我想把鲁迅的著作全读完。
(5) 当主句是以疑问词who或which开头的特殊疑问句时。
如：Who is the boy that is playing football?
正在踢足球的那个男孩是谁？
(6) 当先行词既有人又有物时。
如：Do you remember the people and the things that moved you deeply in 2012? 你还记得2012年那些深深感动你的人和事吗？
 2. 关系代词的省略。一般情况下，that, which, whom作宾语可以省略，但以下情况不能省略：
(1) 关系代词which, whom在从句中作介词宾语时，介词放在which, whom之前，关系代词通常不能省略。
如：I'll never forget the day on which I joined the club.
我永远不会忘记我加入俱乐部的那一天。
(2) that, which, who在从句中作主语时，不能省略。
如：Who is the boy that is talking with our teacher?
正在和我们老师谈话的那个男孩是谁？
You see, you have helped make it possible for me to have “Lucky”， who has filled my life with pleasure.
你知道，你已经帮助我使得我拥有“幸运”，“幸运”使我的生命充满了乐趣。