定语从句 （Attributive Clauses）定语从句：定语从句是由关系代词或关系副词引导的从句,其作用是作定语修饰主句的某个名词性成分,相当于形容词,所以又称为形容词性从句,一般紧跟在它所修饰的先行词后面.
关系代词有：who,whom,whose,that,which等.
关系副词有：when,where,why等.18.1 关系代词引导的定语从句
关系代词所代替的先行词是人或物的名词或代词,并在句中充当主语、宾语、定语等成分.关系代词在定语从句中作主语时,从句谓语动词的人称和数要和先行词保持一致.
1）who,whom,that
这些词代替的先行词是人的名词或代词,在从句中所起作用如下：
Is he the man who/that wants to see you?
他就是你想见的人吗?（who/that在从句中作主语）
He is the man whom/ that I saw yesterday.
他就是我昨天见的那个人.（whom/that在从句中作宾语）2) Whose 用来指人或物,(只用作定语,若指物,它还可以同of which互换）,例如：
They rushed over to help the man whose car had broken down.那人车坏了,大家都跑过去帮忙.
Please pass me the book whose (of which) cover is green.请递给我那本绿皮的书.3）which,that
它们所代替的先行词是事物的名词或代词,在从句中可作主语、宾语等,例如：
A prosperity which / that had never been seen before appears in the countryside.农村出现了前所未有的繁荣.（which / that在句中作宾语）
The package (which / that) you are carrying is about to come unwrapped.你拿的包快散了.(which / that在句中作宾语）2 关系副词引导的定语从句
关系副词可代替的先行词是时间、地点或理由的名词,在从句中作状语.
1）when,where,why
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.任何人都有不得不屈服的时候.
Beijing is the place where (in which) I was born.北京是我的出生地.
Is this the reason why (for which) he refused our offer?这就是他拒绝我们帮助他的理由吗?2）that代替关系副词
that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.他父亲在他出生那年逝世了.
He is unlikely to find the place (that / where / in which) he lived forty years ago.他不大可能找到他四十年前居住过的地方.
3 判断关系代词与关系副词
方法一：用关系代词,还是关系副词完全取决于从句中的谓语动词.及物动词后面无宾语,就必须要求用关系代词；而不及物动词则要求用关系副词.例如：
This is the mountain village where I stayed last year.
I'll never forget the days when I worked together with you.