一. 定義

在復合句中，修飾某一名詞或代詞的從句叫做定語從句。

二. 知識梳理：抓住重點

（一）定語從句所修飾的詞 叫先行詞。 定語從句放在先行詞后面。定語從句分為限定性定語從句和非限定性定語從句。本章只介紹限定性定語從句。引導定語從句的詞有關系代詞that、which、who、 which、 whose和關系副詞where 、when，關系代詞和關系副詞是引導詞， 在定語從句中擔當某一成份。

（二）關系代詞和關系副詞的作用：

①先行詞指物時， 關系代詞用that 或which（在句中作主語或賓語）。如：

China is a country which/that has a large population.

The computer game which/that he is playing is his favorite.

②先行詞指人時， 關系代詞用（who）作主語或賓語，whom (作賓語)，whose (作定語)，that (作主語或賓語)。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.

（三）下列情況下關系代詞只用that 而不用

which 或 who。

１. 先行詞是指物的不定代詞，如：all， little， few， much， none， anything， nothing， everything等時。如：I didn't understand the words all that he said.

2.先行詞由最高級、序數詞以及any， very， only， all， no， just 等所修飾。如：This is the most beautiful place that I have been to .

3. 先行詞既包括人，也包括物。如：They always like to talk about the man and the things that they see on the road.

4. 當主句是以which 或who 開頭的特殊疑問句時。如：Who is the man that opened up the lab.

三. 例題解析：舉一反三

①He is a friend________can help you in time of need.

A. who heB. whose C. / D. who

解析：引導詞在定語從句中做主語，指人。應選D 。

②The most important thing________we should pay attention to is the first thing________ I have said.

A. which， that B. that， which

C. which， whichD. that， that

解析：先行詞前有序數詞， 最高級時，引導次只能用 that. 應選D.

③This is the only one of these books that ________worth reading.

A．has B. haveC. is D. are

解析：引導詞that在句中作主語，代指one ，應選C。

④The man________talked to you just now is my father.

A. whoB. heC. whichD. whose

解析：引導詞在句中作主語指人，應選A.

⑤They thoughttoo much about______.

A. which I had said B. what I had said

C. that I had saidD. I had said

解析：此題引導詞作在從句中作賓語，表示說話的內容，應 選B。