定语从句：是一种用句子作定语修饰名词的主从复合句，通常直接跟在被修饰的名词后面。被修饰的名词称为先行词。定语从句一般由关系代词引导。关系代词连接定语从句和先行词，本身又在定语从句中充当某个成分。例如：

I know the man who spoke to you just now.

先行词 关系代词(who)在定语从句中作主语

我认识刚才和你说话的那个人。

1.关系代词who(m), which,that

who(m)

who引导定语从句修饰表示人的名词，who本身在定语从句中作定语。例如：

The lady who will give us a talk tomorrow is a professor.

明天给我们作报告的女士是位教授。

Tomorrow I'll go to see the man who gave us a lot of help during the trip.

明天我将去看望在旅游中给我们很多帮助的那个人。

The doctor who examined my eyes yesterday morning is well-known in our city.

昨天给我检查眼睛的医生在我们城市很出名。

关系代词whom在定语从句中作宾语，一般可以省略。例如：

Do you know the man (whom) you met at the hotel gate?

你认识我们在旅馆大门口遇见的那个人吗?

The teacher (whom) you want to see has gone home.

你想见的老师已经回家了。

2.which引导的定语从句

which引导的定语从句修饰表示物的名词。which在定语从句中可以作主语或宾语。作宾语时可以省略。例如：

The shop which sells all kinds of sports shoes has closed down.

那家出售各种运动鞋的商店已经关闭。

The film which tells about snakes is interesting.

那部讲述蛇的电影很有趣。

The book (which) he wrote in 1935 still sells well.

他在1935年写的那本书仍然很畅销。

The problem (which) we are trying to work out isdifficult.

我们努力要解出的这道题很难。

Soldiers opened fire on a car which failed to stop at an army checkpoint.

士兵向那辆拒绝在军事检查站停车检查的汽车开了火。

I can't remember which teachers I had.

我记不清哪些老师教过我。

This is a common fallacy which has no basis in fact.

这是一个没有事实依据的常见谬误。

I rewrote his rough draft, which was published under my name.

我把他的草稿重新改写，并以我的名字发表了。(非限制性定语从句)