1.关系代词有who，whom，whose，that和which，关系代词是用来引起定语从句的。
who和whom代表人，在从句中作主语时用who，作宾语时一般用whom：
He is a good physician who cures himself.
能给自己治病的是好大夫。(谚)
Is there anyone who opposes the idea?
有谁反对这个意见?
He is the man whom I met on the train.
他就是我在火车上碰到的那个人。
2.whose表示“他(她)的”，在从句中作定语：
Do you know anyone whose family is in Shanghai?
你认不认识什么人家在上海?
She is the girl whose painting won the first prize.
她就是那个画作赢得头奖的姑娘。
3.which代表事物，在从句中可以作主语(a)或宾语(b)：
a.She told US a story which moved us deeply.
她讲了一个故事使我们深受感动。
Did You see the letter which came this morning?
今天来的那封信你看到了吗?
b.This is the book which I told you about.
这就是我和你谈到的那本书。
This is a factor which we must consider.
这是我们必须考虑的一个因素。
4.that代表事物的时候较多(a)，有时也可以代表人(b)：
a.Have you got everything that you need?
你需要的东西都带了吗?
They lived in a house that was built in 1600.
他们住在一栋1660年盖的房子里。
b.Who is the man that's sitting by her side?
坐在她旁边的那个人是谁?
5.定语从句分限制性的和非限制性两种。在限制性定语从句中，当关系代词在从句中作宾语时，常常可以省略，特别是在口语中：
These are the tickets I bought for you.
这是我替你买的票。
Is there anything you want to say?
你有什么话要说吗?
在非限制性定语从句中，关系代词不能省略，而且不能用that。
