1．定語從句在句中作定語用，修飾句中的某一名詞（或代詞），被定語從句所修飾的詞叫先行詞。定語從句必須放在先行詞之后。引導定語從句關聯詞有：
關系代詞：who，whom，whose，which，that
關系副詞：when，where，why, that等。
⒈定語從句試題，主要考查使用關系詞的能力。
○1找出被修飾的先行詞，分析關系詞在從句中的語法作用，確定關系代詞：
This is the hospital（that）we visited yesterday．
此句的先行詞為hospital,可用which／that，但不可用who，whom。關系詞在從句中作visit的賓語，不可用where。
又如：We visited a factory＿which or that＿makes toys for children.
We visited the factory __where__ Li Ming’s father once worked.
○2掌握 which和that使用上的區別。
a. 只能用which的情況：
（l）先行詞是物時，介詞后的關系代詞應用which，不用that。
This is the home in which（＝where）Lu Xun once lived.
若介詞不前置,用that也可。
如：The room which／that we live in is clean．
（2）在非限制性定語從句中，關系代詞用which．
Last night I saw a very good film, which was about the Anti-Japanese War.
（3）先行詞為物，且被that或those修飾時，通常用which。如：
That book which Tom bought yesterday is useful.
b.在下列情況下，一般用that。
（1）先行詞為all, everything, nothing，something，anything，little，no，much，the only，the same，the very，the first，the last，any，every時。如：
Is there anything（that）1 can do for you in town？
He was the only teacher（that）I knew in your schoo1．
（2）先行詞為形容詞最高級所修飾時。
This is one of the most exciting football games (that) I have ever seen.
It was the finest art exhibition that we ever saw.
先行詞中既有人，也有物時。如：
Can you see a man and his horse that are crossing the bridge?
○3用詞不可重復。定語從句中，己有關系詞作主語、賓語或狀語時，不可再重復。如：
The man＿＿＿＿was a friend of mine！
A. that you just talked to B. whom you just talked to him
C. who you just talked to him D. which you just talked to
○4as 和which可代表全句意思，但其用法有差別。它們引導非限制性定語從句，可以用整個主句作為先行詞，指代上面或下面所說的一件事。區別如下：
a. as引導的從句可放在主句之前或之后，而which只可放在主句之后。如：
As is known to us all, we have made great progress in science and technology.
Tom failed in the exam, which made us so sorry.
b. 從句中的謂語動詞是describe, do, tell, know, expect，see, hear, watch, say, show等實義動詞時，用as.
As we all know, Shakespeare is a famous writer.
To shut your eyes to facts, as many of you do, is foolish.
There is great disorder, as the newspapers will have told you.
c. 當從句的謂語動詞是否定形式或從句謂語帶有一個復合賓語結構時，一般用which而不用as。
如：
You pretended not to know me, which I didn’t understand.
He admires everyone in the class, which I find quite strange.
d. as 作關系代詞常與the same, such配合使用。
如：
I had the same things as you.
Metals are such things as iron, silver and gold.
○5 介詞加關系代詞中介詞的選用
（1） 根據與先行詞的習慣搭配。
I will never forget the day on which I joined the Party.
（2） 根據和從句中動詞的固定搭配。
This is not the dictionary of which the teacher spoke in class.
（3） 根據句子的具體意義。
He invented a telescope, with which he could study the sky.
○6使用定語從句應注意的幾個問題：
（1）關系代詞在從句中作主語時，從句的謂語動詞用單數還是復數應由先行詞決定。
The mm who lives downstairs speaks English fluently.
The students who are in Grade Three are going to climb the hi11 tomorrow。
(2)定語從句有時不直接緊靠著先行詞，中間由一個定語、狀語或謂語隔開。
如：
There is an expression in his eyes that I can’t understand．
The days are gone forever when the Chinese people were looked down upon。
(3)引導定語從句的關系副詞可以用“介詞+which”來代替。
如：
0ctober l，1949 was the day on which（=when）the People’s Republic of China was founded.
(4)當定語從句中謂語動詞是帶介詞或副詞的短語動詞時，短語動詞的各個固定的部分不要拆開。
The dictionary which you are looking for is on the desk.
The sick man whom she is 1ooking after is her father.