引导定语从句的关系代词有who, whom, whose, which, that, as 和 关系副词 when, where, why。
1．Who （人， 主格，从句中作主语，非正式文体中代替whom作宾语，但是如果关系代词作介词的宾语，介词提前，就不用who，而用whom）
The person to whom you spoke is a famous actor.
The person who(whom) you spoke to is a famous actor.
2．Whom （人， 宾格，从句中作宾语，非正式文体中常省略）
3．Whose （多指人，也可物，指物可以与of which互换，从句中作定语）
He mentioned a book whose author (= the author of which) I can't remember now.
She sat on the corner of the table near the door by which her husband always entered.
She sat on the corner of the table near the door which her husband always entered by.
This is the key which you are looking for.
I'll never forget the day which I first met you on. (Χ)
I have the book you are talking about.
The girl he leaned against was his sister.
5. that （指人，也可物，从句中作主语或宾语，还可以作表语，作宾语或表语可以省略）
He is not the man that he used to be.
The house that we live in is not large.
The house in which we live is not large.
The house we live in is not large.
1）由不定代词anything, nothing, everything, all, one, little, few, much等充当先行词时。
2）先行词被all, every, no, some, any, little, much 等修饰。
4）先行词被the only, the very, the same, the last 修饰时。
That white flower is the only one that I really like.
This is the very book that I want to have.
The last place that we visited was the chemical works.
He talked about the teachers and schools that he had visited.
6）当主句是以who, which 开头的特殊疑问句时，定语从句多用that,而不用who(whom),which.
Who is the person that is standing at the gate?
常用于 the same--- as, such ---as, as --- as , so --- as
但 as 引导从句表示内容与主句相似，同类；that 表示内容与主句同一，同一事物。
This is the same bag as I lost yesterday. This is the same bag that I lost yesterday.
Such --- as 可以放在一起以such as 形式放在名词后。
She collected a great many stories such as a child of four could understand.
As we have seen, oceans cover more than 70 % of the earth.
As is known to all, Taiwan is a part of China.
1）关系副词when, where, why的含义相当于“介词+ which”结构，因此常常和“介词+ which”结构交替使用。例如：
There are occasions when （on which）one must yield.
Beijing is the place where（in which）I was born.
Is this the reason why （for which）he refused our offer?
2）that代替关系副词，可以用于表示时间、地点、方式、理由的名词后取代when, where, why和“介词+ which”引导的定语从句，在口语中that常被省略。例如：
His father died the year （that / when / in which） he was born.
He is unlikely to find the place （that / where / in which） he lived forty years ago.
This is the house which we bought last month.
The house, which we bought last month, is very nice.
Charles Smith, who was my former teacher, retired last year.
My house, which I bought last year, has got a lovely garden.
This novel, which I have read three times, is very touching.
3）非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数，例如：
He seems not to have grasped what I meant, which greatly upsets me.
Liquid water changes to vapor, which is called evaporation.