定语从句所修饰的词叫先行词。
定语从句放在先行词后面。
定语从句分为限定性定语从句和非限定性定语从句。
本章只介绍限定性定语从句。
引导定语从句的词有关系代词that、which、who、which、whose和关系副词where 、when，关系代词和关系副词是引导词，在定语从句中担当某一成份。
关系代词和关系副词的作用：先行词指物时，关系代词用that 或which（在句中作主语或宾语）。
如：China is a country which / that has a large population.The computer game which/ that he is playing is his favorite.先行词指人时，关系代词用（who）作主语或宾语，whom (作宾语)，whose (作定语)，that (作主语或宾语)。
如：The man who is mending the machine has been retired.This is the policeman who/ whom they were talking about yesterday.I like the girl whose mother is an actor.注意：下列情况下关系代词只用that 而不用which 或who。
先行词是指物的不代词，如：all, little, few, much, none, anything, nothing, everything等时。
如：I didn't understand the words all that he said.2．先行词由最高级、序数词以及any, very, only, all, no, just 等所修饰。
如：This is the most beautiful place that I have been to .行词既包括人，也包括物。
如：They always like to talk about the man and the things that they see on the road.当主句是以which 或who 开头的特殊疑问句时。
如：who is the man that opened up the lab.例题解析：举一反三，学的更轻松！He is a friend ______ can help you in time of need.A. who heB. whoseC. /D. who解析：引导词在定语从句中做主语，指人。
应选D 。
The most important thing ______ we should pay attention to is the first thing ______ I have said.A. which, thatB. that, whichC. which, whichD. that, that解析：先行词前有序数词，最高级时，引导次只能用that. 应选D.This is the only one of these books that ______worth reading.A．has B. have C. is D. are解析：引导词that在句中作主语，代指one ，应选C。
The man ______ talked to you just now is my father.A. whoB. heC. whichD. whose解析：引导词在句中作主语指人，应选A.They thought too much about ______.A. which I had saidB. what I had saidC. that I had saidD. I had said解析：此题引导词作在从句中作宾语，表示说话的内容，应选B。
一、选择最佳答案填空：1．Did you find the notebook ______ Jim had given me for my birthday?A. whoB. whomC. whichD. whose2. That's all ______ I have seen and heard.A. whichB. thatC. whereD. what3. Have you seen the man ______ plan we were talking about ______ yesterday ?A. who, themB. its, themC. whose,/D. whose, them4.The Oscar is one of the film prizes ______ offered to any Chinese actor or actress so far.A. which are notB. that have not beenC. that has notD. that has not been5. He never reads anything ______ is not worth reading.A. thatB. asC. whoD. which6. The man ________ coat is black is waiting at the gate.A. who'sB. whoseC. thatD. of which7. _________ cleans the classroom can go home first.A. AnyoneB. those whooC. HoweverD. The one who8. The police caught the man _______ stole my handbag.A. heB. thatC. whomD. which9. The girl ________ is reading under the tree ________ my sister.A. which, isB. whom, wasC. who , isD. who, was10. George Mallory was an English teacher _______ loved climbing.A. whoB. whomC. heD. which1-5 CDCBA 6-10 BDBCA关系词引导定语从句的关联词称为关系词，关系词有关系代词和关系副词。
关系代词有that, which, who, whom, whose, as等，绝对没有what；关系副词有where, when, why等。
关系词常有3个作用：①连接作用，引导定语从句。
②代替主行词，甚至可能是主句中的一部分或者整个主句。
③在定语注：关系代词有主语、宾语之分。
一般whom作为宾语。
关系代词在从句中作主语，宾语，表语，定语等，关系副词在从句中作地点状语，时间状语，原因状语。
定语定语用来限定、修饰名词或代词起修饰、限定作用的词、短语（动词不定式短语、动名词…的’表示容词担任，此外，名词，代词，数词，分词，副词，不定式以及介词短语也可以来担任，也可以由一个句子来担任。
单词作定语时通常放在它所修饰的词之前，作前置定语被定语从句修饰的名词、代词称为先行词。
如The man The book关系代词所代替的先行词是人或物的名词或代词，并在从句中充当主语、宾语、定语等成分。
关系代词在定语从句中作主词保持一致。
1,who, whom, that这些词代替指人，whom作宾语指人，that既可作主语又可作宾语（作宾语可以省略），可以指人也可以指物。
在从句中所起作用如下：(1) Is he the man who/that wants to see you? 他是那个想见你的男人吗？（who/that在从句中作主语）(2) He is the man whom/ that I saw yesterday. 他就是我昨天见的那个人。
（whom/that在从句中作宾语）（3）The man whom you spoke to just now is our English teacher 你刚刚说话的那个男人是我们的英语老师2,Whose 用来指人或物(只用作定语, 等，作宾语时可以省略，例如：(1)Prosperity which / that had ne ppears in te. 农村出现了前所未有的繁荣。
（which / that在从句中作主语）(2) The package (which / that) you are carrying is about to come unwrapped.你拿那个包裹快要散开了。
(which / that在从句中作宾语）whosewhose表示谁（可以为人也可以为物）的（东西）例：A child whose parents are dead is called an arphan.双亲都死了的孩子叫做孤儿。
(whose表示那个孩子的双亲)He lives in a room whose window faces south.他住的那个房子的窗户是朝南的。
（whose表示那个房子的窗户）关系代词：在句中作主语、宾语或定语1. that既可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从省略。
[eg：This is the book （which）you want.]2不及物动词+介词”的介词的宾语代词wh放在它原来的位置3. 代表物时多这时的that常被省略；c被形容词最高级修饰时；既有人又有物时；e)整个句中前面已有which，wh行关系副词：在句中作状语关系副词=介词+关系代词why=for whichwhere=in/ at/ on/ich (介词同先行词搭配)when=during/ on/ in/ ... which (介词同先行词搭配)1. where是关系代词，当然也不用that引导。
By the time when you arrived in London, we had stayed there for two weeks. 到你到达伦敦的时候，我们在那里已经待了两个星期。
I still remember the her. 我仍然记得我第一次见到她。
Each time when he goes to business trip, he brings a lot of living necessities, such as towels, soap, toothbrush etc。