关系代词有 that, which, who, whom, whose, as 等；关系副词有 where, when, why 等。
关系词通常有 2 个作用：一是引导定语从句。二是代替先行词并在定语从句中担当一个成分。
- who 指人，在从句中做主语。
The boys who are playing football are from Class One.
- whom 指人，在定语从句中充当宾语，常可省略。Mr. Liu is the person (whom) you talked about on the bus. The man whom you met just now is my friend.
- which 指物，在定语从句中做主语或者宾语，做宾语时可省略。
Football is a game which is liked by most boys. This is the pen (which) he bought yesterday.
- that 指人时，相当于 who 或者 whom；指物时，相当于 which。
The number of the people that/who come to visit the city each year rises one million. Where is the man that/whom I saw this morning?
- whose 通常指人，也可指物，表示所属关系，在定语从句中做定语。
He has a friend whose father is a doctor.
I once lived in a house whose roof has fallen in.
The school (that/which) he once studied in is very famous. The school in which he once studied is very famous.
Tomorrow I will bring here a magazine (that/which) you asked for. Tomorrow I will bring here a magazine for which you asked.
We'll go to hear the famous singer (whom/that/who) we have often talked about. We'll go to hear the famous singer about whom we have often talked.
- 含有介词的动词短语一般不拆开使用，如：look for, look after, take care of 等
This is the watch which/that I am looking for.
- 若介词放在关系代词前，关系代词指人时用 whom，不可用 who 或者 that；指物时用 which， 不能用 that；关系代词是所有格时用 whose
The man with whom you talked is my friend.
The plane in which we flew to Canada is very comfortable.
- “介词+关系代词”可有 some, any, none, both, all, neither, most, each, few 等代词或者数词
He loved his parents deeply, both of whom are very kind to him.
In the basket there are quite many apples, some of which have gone bad. There are forty students in our class in all, most of whom are from big cities.
- when 指时间，在定语从句中做时间状语
I still remember the day when I first came to the school. The time when we got together finally came.
- where 指地点，在定语从句中做地点状语
Shanghai is the city where I was born.
The house where I lived ten years ago has been pulled down.
- why 指原因，在定语从句中做原因状语
Please tell me the reason why you missed the plane. I don't know the reason why he looks unhappy today.
The reason why/ for which he refused the invitation is not clear,
From the year when/in which he was going to school he began to know what he wanted when he grew up. Great changes have taken place in the city in which/where I was born.
The teacher told me that Tom was the only person that I could depend on. China is a country which has a long history.
His mother, who loves him very much, is strict with him.
China, which was founded in 1949, is becoming more and more powerful.
His brother who is now a doctor always encourages him to go to college.
His brother, who is now a doctor, always encourages him to go to college.
（一）限制性定语从句只能用 that 的几种情况
- 当先行词是 anything, everything, nothing (something 除外), few, all, none, little, some 等代词时， 或者是由 every, any, all, some, no, little, few, much 等修饰时
Have you taken down everything that Mr. Li has said?
There seems to be nothing that seems impossible for him in the world. All that can be done has been done.
There is little that I can do for you.
The first place that they visited in London was the Big Ben.
This is the best film that I have seen.
- 当形容词被 the very，the only 修饰时
This is the very dictionary that I want to buy,
After the fire in his house, the old car is the only thing that he owned.
- 当先行词前面有 who, which 等疑问代词时
Who is the man that is standing there? Which is the T-shirt that fits me most?
Can you remember the scientist and his theory that we have learned?
（二）关系代词 as 和 which 引导的定语从句
as 和 which 引导非限制性定语从句，有相同之处也有不同之处。具体情况是： 1．As 和 which 都可以在定语从句中做主语或者宾语，代表前面整个句子。He married her, as/which was natural.
He was honest, as/which we can see.
- as 引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which 引导的非限制性定语从句只能放在主句之后。另外，as 有“正如„„，正像„„”的意思
As is known to all, China is a developing country. He is from the south, as we can see from his accent. John, as you know, is a famous writer.
He has been to Paris more than several times, which I don't believe.
- 当先行词受 such, the same 修饰时，常用 as I have never heard such a story as he tells.
He is not such a fool as he looks.
（三）以 the way 为先行词的定语从句通常由 in which, that 引导，而且通常可以省略。
The way in which/ that/./ he answered the question was surprising.