定语从句：所谓从句就是一个主谓结构相当于整个句子的一个成分，因此从句不能单独使用。在复合句中修饰名词或者代词，做定语的句子叫定语从句

如   1) The man who lives next to us is a policeman

              2) You must do everything that I do.

     上面两句中的man和everything 是定语从句所修饰的词。定语从句修饰的词叫先行词，因为它总是处在定语从句的前面，比定语从句先行一步.引导定语从句的词叫关系词，包括关系代词that, which, who( 宾格whom, 所有格whose)和关系副词where, when, why.

      关系词常有三个作用:1. 引导定语从句   2. 代替先行词    3.在定语从句中担当一个成分

二 关系代词引导的定语从句

      1. who指人，在从句中做主语

   The boys who are playing football are from Class One.

2. 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

   关系代词whom在口语和非正式语体中常用who代替，可省略

3. which 指物，在定语从句中做主语或宾语，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.(做宾语可省略)

4. that 指人时，相当于who或者whom, 指物时相当于which在定语从句中做主语或者宾语，做宾语时可省略

  The people that/ who come to visit the city are all here.

  Where is the book that/ which I read this morning?

5. Whose通常指人，也可指物，在定语从句中做定语

  He has a friend whose father is a doctor. 

三 关系副词引导的定语从句

  I will never forget the day when(on which) I joined the League.

         He will go back to the school where(in which) he studied next week.

         I don’t know the reason why( for which) he quarreled with Zhanglin