在復(fù)合句中 ， 修飾名詞或代詞的從句叫定語(yǔ)從句 ， 被修飾的名詞或代詞叫先行詞 ， 引導(dǎo)定語(yǔ)從句的有關(guān)系代詞 who, whom, whose, which, that等和關(guān)系副詞where, when, why等 ， 關(guān)系代詞和關(guān)系副詞在定語(yǔ)從句中擔(dān)任句子成份。
1.由who引導(dǎo)的定語(yǔ)從句中 ， who用作主語(yǔ) ， 如 ： This is the boy who often helps me.
2.由whom引導(dǎo)的定語(yǔ)從句中，whom用作賓語(yǔ)，如：The man whom you are waiting for has gone home.
3.由whose引導(dǎo)的定語(yǔ)從句中 ， whose用作定語(yǔ) ， 如 ： Do you know the girl whose skirt is white?
4.由which引導(dǎo)的定語(yǔ)從句中，which用作主語(yǔ)或謂語(yǔ)動(dòng)詞的賓語(yǔ)或介詞的賓語(yǔ)，如：
The room in which there is a machine is a work shop.
The river which is in front of my house is very clean.
This is the pen which you want.
注意 ：
(1)whom, which用作介詞賓語(yǔ)時(shí) ， 介詞可放在 whom、which之前 ， 也可放在從句原來(lái)的位置上；但在含有介詞的動(dòng)詞固定詞組中，介詞只能放在原來(lái)的位置上。如： He is the very person whom we must take good care of.
(2)引導(dǎo)非限制性定語(yǔ)從句時(shí)，必須用關(guān)系代詞which，不用that,如：I have lost
my bag, which I like very much.
(3)關(guān)系代詞在句中作主語(yǔ)時(shí)，從句的謂語(yǔ)動(dòng)詞的人稱和數(shù)必須和先行詞保持一致。
5.由that引導(dǎo)的定語(yǔ)從句中，that可以指人或物，在從句中作主語(yǔ)或謂語(yǔ)動(dòng)詞的賓語(yǔ)，但不能放在介詞后面作介詞賓語(yǔ)，如：
The book that I bought yesterday was written by Lu Xun.
注意在下面幾種情況下必須用 that引導(dǎo)定語(yǔ)從句。
(1)先行詞是不定代詞all, few, little, much, something, nothing, anything等 ， 如 ：
All that we have to do is to practise English.
(2)先行詞被序數(shù)詞或形容詞級(jí)所修飾，如
The first letter that I got from him will be kept.
(3)先行詞被all, any, every, each, few, little, no, some等修飾 ， 如
I've eaten up all the food that you gave me.
(4)先行詞被the only, the very, the same, the last修飾時(shí)如
He is the only person that I want to talk with.
(5)先行詞既有人又有物時(shí)，如:
They talked about persons and things that they met.
(6)當(dāng)句中已有who時(shí) ， 為避免重復(fù) ， 如 ： Who is the man that is giving us the
class?
6.由when, where, why引導(dǎo)的定語(yǔ)從句，如:
I don't know the reason why he was late.
This is the place where we have lived for 5 years.
I'll never forget the day when I met Mr Li for the first time.
注意：先行詞是表示地點(diǎn)時(shí)，如果從句的謂語(yǔ)動(dòng)詞是及物的，就用 that(which)，如果從句的謂語(yǔ)動(dòng)詞是不及物的，就用where引導(dǎo)。This is the house Which /that he has lived in for 15 years.(Where he has lived for 15 year.)
7. 限制性定語(yǔ)從句和非限制性定語(yǔ)從句
(1)限制性定語(yǔ)從句是句中不可缺少的組成部分，主句和從句之間不用逗號(hào)分開(kāi)。引導(dǎo)非限制性定語(yǔ)從句的關(guān)系代詞有who, whom, whose, which, of which等，這些關(guān)系代詞都不能省略。
(2)非限制性定語(yǔ)從句是對(duì)主句先行詞的補(bǔ)充說(shuō)明 ， 沒(méi)有這種從句 ， 不影響主句意思的完整 ， 一般用逗號(hào)把主句和從句分開(kāi) ， 關(guān)系代詞用 which,不用that;指人時(shí)可用who,如 ： I have two brothers, who are both students.
8．如何簡(jiǎn)化定語(yǔ)從句
（1）.定語(yǔ)從句簡(jiǎn)化為形容詞或形容詞短語(yǔ)作后置定語(yǔ)。如:
My grandfather lives in a village that is far away from here.
→My grandfather lives in a village far away from here.我祖父住在離這兒很遠(yuǎn)的一個(gè)村子。
This is a book that is worth reading.
→This is a book worth reading. 這是一本值得看的書(shū)。
（2） 定語(yǔ)從句簡(jiǎn)化為現(xiàn)在分詞或現(xiàn)在分詞短語(yǔ)作前置或后置定語(yǔ)。
The man who is standing under the tree is our English teacher.
→The man standing under the tree is our English teacher.
站在樹(shù)下面的那個(gè)人是我們的英語(yǔ)老師。
I saw the house that was burning at that time.→I saw the burning house at that time.
當(dāng)時(shí)我看到那房子在燃燒。
（3）定語(yǔ)從句簡(jiǎn)化為過(guò)去分詞短語(yǔ)作后置定語(yǔ)。
I like to see the films which are directed by Zhang Yimou.→I like to see the films directed by Zhang Yimou. 我喜歡看張藝謀導(dǎo)演的電影。
She is the girl who was praised at the school meeting.→She is the girl praised at the school meeting. 她就是在校會(huì)上受表彰的那個(gè)女孩。
（4）定語(yǔ)從句簡(jiǎn)化為不定式作后置定語(yǔ)。
He is always the first person that comes to school.→He is always the first person to come to school.他總是第一個(gè)到校。
The report which will be given tomorrow is important to us.→The report to be given tomorrow is important to us. 明天要作的報(bào)告對(duì)我們很重要。
（5）定語(yǔ)從句簡(jiǎn)化為what 從句。
I couldn't remember the words that he said.→I couldn't remember what he said.
我記不得他說(shuō)的話。
【典型例題解析】
例 1 The second book ______I want to read is Business @ the Speed of Thought.
A. which B. what C. that D. as
解析 先行詞 book被序數(shù)詞修飾時(shí)要用that引導(dǎo)定語(yǔ)從句，故選C。
例 2 I'll never forget the days _____I stayed with you.
A. when B. in which C. that D. for which
解析 本題指時(shí)間，故選 A。
例 3 The book______ is sold out at the moment.
A. you need B. what you need
C. which you need it D. that you need it
解析 B、C、D中的what和it與先行The book相抵觸 ， 故選 A。
例 4 Is this the place ______Lincoln once lived.
A. that B. which C. where D. when
解析 本題指地點(diǎn)，故選 C。
例 5 I'm one of the boys _________ never late for school.
A. that is B. who are C. who am D. who is
解析 本題中 who用作主語(yǔ)，謂語(yǔ)動(dòng)詞與先行詞the boys保持一致，故選B。
【選講例題】
例 6 Her sister,______ you met at my home, was a teacher of English.
A. whom B. that C. which D. who is
解析 非限制性定語(yǔ)從句中 ， 關(guān)系代詞用 which,不用that,但指人時(shí)用who或whom.故選A。
例 7 These book are for students _____ mother language is not English.
A. of whom B. that C. which D. whose
解析 whose引導(dǎo)的定語(yǔ)從句中,whose用作定語(yǔ)，故選D。