引導(dǎo)定語從句的有：關(guān)系代詞who(whom, whose)，which, that和關(guān)系副詞when, where, why等。例如：
the girl who had lunch with me yesterday is my girl friend.昨天與我共進午餐的那個女孩是我的女朋友。(girl是先行詞，who是關(guān)系代詞)
the book that(which)i am reading is very interesting.我正在看的這本書非常有趣。(book是先行詞，that是關(guān)系代詞)
現(xiàn)略談一談關(guān)系代詞和關(guān)系副詞的作用和用法，引導(dǎo)定語從句的關(guān)系代詞和關(guān)系副詞在先行詞和定語從句之間起聯(lián)系作用，它們可以作定語從句的一個成分：
一、關(guān)系代詞可以作定語從句的主語、賓語或定語。
1.who指人，是主格，在定語從句中作主語；whom是賓格，在定語從句中作賓語；whose是所有格，在定語從句中作定語。例如：
(1)this is uncle li who mended computers for us.這就是為我們修電腦的李叔叔。
the student who(that)is playing with a yoyo is only seven.正在玩溜溜球的那個學(xué)生僅僅七歲。
(2) this is the man(whom)i met in australian last month.這就是我上個月在澳大利亞遇見的那個人。
the soldier whom you want to see has already come.你要見的那名士兵已經(jīng)來了。
(3)there is nobody here whose name is gu jianfei.這兒沒有名叫顧劍飛的人。
my aunt whose photo i showed you yesterday will come to see us this evening.我姨媽今晚要來看我們，她的照片昨天我給你看過。
2.which指物，在定語從句中作主語或賓語。例如：
(1)take the pencil which is lying on the desk.把課桌上的那支鉛筆拿去。
we visited the jade buddha temple, which is in the northwestern part of shanghai.我們參觀了玉佛寺，它在上海西北邊。
(2)the factory which we visited yesterday is very famous in the world.我們昨天參觀的那家工廠是全球聞名的。
the money which they found in the street is mine.他們在街上找到的錢是我的。
3.that指物，有時也指人，在定語從句中作主語或賓語。指物時，它的用法和which大致相同。例如：
(1)the comrade that you saw is a combat hero.你見到的那個同志是個戰(zhàn)斗英雄。(that作賓語，指人)
is this the pen that you were looking for@你要找的鋼筆是這一支嗎@(that作賓語，指物)
(2)the man that called me last night was killed this morning.昨夜給我打電話的那個人今早給人殺了。(that作主語，指人)
there is no difficulty that cannot be overcome.沒有不能克服的困難。(that作主語，指物)
[注1]that和which都指事物時，一般可以通用。但在下列情況下必須用that，而不能用which:
1先行詞為all，everything, nothing, something, anything, much little, few, none, the one等時。例如：
say all(that)you know.把你知道的全部講出來。
is there anything(that)i can do for you now@現(xiàn)在需要我為你做點什么嗎@
this book contains much little that is useful.這本書中有很多(沒有多少)有用的東西。
i mean the one that was bought yesterday.我指的是昨天買的那個。
2先行詞為數(shù)詞或被序數(shù)詞(含last)修飾時。例如：
this is the first film(that)i have seen since i came here.這是我到這里以來所看的第一部電影。
the last place they visited was the summer palace.他們最后參觀的地方是頤和園。
look at those presents. you can see the two that you gave me.看那些禮物，你能看見你送我的那兩個嗎@
3先行詞被形容詞的最高級或the very, the only等所修飾時。例如：
this is the biggest apple(that)i have ever eaten.這是我所吃到的蘋果中最大的一個。
she is the very thief(that)the policeman is looking for.她就是警察正在尋找的那個小偷。
mary is the only friend(that)i have in australia.瑪麗是我在澳大利亞唯一的朋友。
4先行詞中既有人又有物時。例如：peter and his car that disappeared mysteriously in london in 1987 appeared mysteriously in new york in 1993.彼得和他的小轎車1987年在倫敦神秘地失蹤，后來于1993年又神秘地出現(xiàn)在紐約。
we were deeply impressed by the teachers and schools that we had visited.我們訪問過的老師和參觀過的學(xué)校給我們留下了深刻的印象。
5先行詞在主句中作表語，或關(guān)系代詞在從句中作表語時。例如：
this is a dictionary that will help you a lot.這是本對你很有幫助的字典。
don't cheat me. i'm no longer the boy that i was three years ago.別騙我了，我再也不是三年前的我了。
[注2]在下列情況下不宜用that:
1.關(guān)系代詞前有介詞時。例如：
this is the house in which i lived ten years ago.這就是我十年前住過的房子。
2.先行詞本身是that時。例如：
what was that which he said@他說了些什么@
[注3]whom,which和that在定語從句中作賓語時，特別是在口語中，往往可以省略。例如：
the man(that)you got the news from is a friend of mine.告訴你這個消息的人是我的朋友。
is that the car(which)you want to buy@那就是你所要買的汽車嗎@
this is the little boy(whom)comrade li saved yesterday.這就是李同志昨天救的那個小男孩。
二、關(guān)系代詞whom, which在定語從句里作介詞的賓語時，介詞一般放在先行詞與關(guān)系代詞之間。例如：
i want to make some friends from whom i can learn a lot.我想交幾個朋友，從他們那兒我可以學(xué)許多東西。
但是，有時介詞也可以放在賓語從句的后面，特別是在省略了關(guān)系代詞時，介詞必須放在定語從句的后面。例如：
the room which(that)we live in is very bright.
the room we live in is very bright.我們住的那間房間很明亮。
三、關(guān)系代詞which有時指整個前面一句話。這時關(guān)系代詞前面有逗號，定語從句是附加的說明；which的意思相當(dāng)于and this。例如：
tom said he didn't know anything about kate, which was a lie.湯姆說他對凱特的情況一無所知，這是撒謊。
the worker didn't do any work，which made his boss very angry.那個工人什么活也沒干，這令老板非常生氣。
四、關(guān)系副詞where, when和why在定語從句中分別作地點狀語、時間狀語和原因狀語。
1.where指地點，在定語從句中作狀語，相當(dāng)于in等＋which。例如：
this is the workshop where(=in which)i work.這是我工作的車間。
a booking office is a place where(=in which)tickets are sold.售票處就是賣票的地方。
2.when指時間，在定語從句中作狀語。例如：
he came at a time when we needed help.他在我們需要人幫忙的時候來到了。
3.why指原因、理由，在定語從句中作原因狀語。例如：
the reason(why)he changed his mind is not clear.他改變主意的原因尚不清楚。下面再略談一談限制性定語從句和非限制性定語從句。限制性定語從句是先行詞不可缺少的定語，如果省去，主語的意思就會不完整或不明確。這種從句和主句之間不能用逗號分開。非限制性定語從句，只是對先行詞的附加說明，如果省去，主句的意思仍然很清楚，它和主句之間常用逗號分開。試比較下列句子：
(1)i have a brother who is a doctor.我有一個當(dāng)醫(yī)生的兄弟。(意思是我還有其他兄弟)(限制性定語從句)
(2)i have a brother, who is a doctor.我有一個兄弟，是個醫(yī)生。(意思是我只有一個兄弟)(非限制定語從句)
[注1]在非限制性定語從句里不宜用關(guān)系代詞that。因此，凡是that所引導(dǎo)的定語從句，一般都是限制性定語從句。例如：
誤：she gave me some flowers, that were very beautiful.
正：she gave me some flowers, which were very beautiful.(非限制性定語從句)
正：she gave me some flowers that(which)were very beautiful.(限制性定語從句)
[注2]非限制性定語從句在口語里很少用，尤其是在對話里，經(jīng)常是采用簡單句或并列句。例如：“i have a brother, who is a doctor.”這句話，在口語里總是說：“i have a brother; he is a doctor.”或說：“i have a brother, and he is a doctor.”
