定义：在复合句中，修饰名词或代词的从句叫定语从句。
温馨提示：被修饰的名词或代词叫先行词，引导定语从句的有关系代词 who, whom, whose, which, that等和关系副词where,when, why等，关系代词和关系副词在定语从句中担任句子成份。
1.由who引导的定语从句中，who用作主语。
如： This is the boy who often helps me.
2.由whom引导的定语从句中，whom用作宾语。
如：The man whom you are waiting for has gone home.
3.由whose引导的定语从句中， whose用作定语。
如：Do you know the girl whose skirt is white?
4.由which引导的定语从句中，which用作主语或谓语动词的宾语或介词的宾语。
如： The room in which there is a machine is a work shop.
注意：
(1)whom, which用作介词宾语时，介词可放在 whom、which之前，也可放在从句原来的位置上；但在含有介词的动词固定词组中，介词只能放在原来的位置上。
如：He is the very person whom we must take good care of.
(2)引导非限制性定语从句时，必须用关系代词which，不用that。
如：I have lost my bag, which I like very much.
(3)关系代词在句中作主语时，从句的谓语动词的人称和数必须和先行词保持一致。
5.由that引导的定语从句中，that可以指人或物，在从句中作主语或谓语动词的宾语，但不能放在介词后面作介词宾语，如：
The book that I bought yesterday was written by Lu Xun.
【典例分析】
1. The young man _____ is an engineer of our factory．
A．that you just talked
B．whom you just talked to
C．which you just talked to
D．who you just talked
【答案】B
【解析】
试题分析：句意：刚才和你交谈的那个年轻人是我们工厂的一名工程师。此题考查定语从句，the young man在定语从句中做宾语，根据句意，故选B。
考点：考查定语从句
2. This is the school _______ you studied when you were young.
A. which
B.what
C. in which
D. whom
【答案】C
考点：考查定语从句。
