定语从句:  在复合句中修饰名词或代词的句子在复合句中充当定语，所以叫作定语从句。

先行词：  定语从句所修饰的名词或代词。

关系词：  引导定语从句的词，分为关系代词（who,whom,that,which,whose）和关系副词(where,when,why,)。

     复合句 ：    The man   who (that) came is Mike.

                   先行词   关系代词

Li Ming is the one  that   got full marks in our class.

    先行词 关系代词

          上句的黑体字为复合句中的主句，蓝体字为定语从句.

一 定语从句的关系代词 Which的用法: 若先行词指物则代替先行词在定语从句中充当主语或宾语.

      This is the pen   which  was given by my friend.

            先行词   指物代替先行词在定语从句中充当主语

      This is the pen   which my friend gave to me.

            先行词   指物代替先行词在定语从句中充当宾语

二 定语从句的关系代词 Who的用法: 若先行词指人则代替先行词在定语从句中充当主语或宾语(如果前面带介词则必须用whom)

The man who is wearing a white suit is my brother.

先行词   指人代替先行词在定语从句中充当主语

The man who\whom he wanted to see last week is in Shanghai.

先行词   指人代替先行词在定语从句中充当宾语

She is the girl with whom I went there.

先行词     指人代替先行词在定语从句中充当介宾且介词于前.

三 定语从句的关系代词 Whom的用法: 若先行词指人则代替先行词在定语从句中充当宾语(包括介词的宾语) ,与who的区别是如果前面带介词则必须用whom

This is the teacher whom\who we like best.

      先行词   指人代替先行词在定语从句中充当宾语

She is the girl whom\ who I went with there.

先行词  指人代替先行词在定语从句中充当介宾.

   I don’t like the boy to whom you are talking.

 先行词 指人代替先行词在定语从句中充当介宾且介词于前.

四 定语从句的关系代词 that的用法: 若先行词指人或物则代替先行词在定语从句中充当主语或宾语

   The animal that \which is lost is a panda.

先行词   指物代替先行词在定语从句中充当主语

She is the person that \who we are worried about.

先行词   指人代替先行词在定语从句中充当宾语

注意1 that \which在代物时常常可以通用,但有时只宜于用which ,不用that

(1)     关系代词前有介词时.

This is the hotel in which you will stay.

(2)     如有两个定语从句,其中一句的关系代词是that,另一句宜于用which.

Let me show you the novel that I borrowed from the liberary which was newly open (新开放) to us.

注意2that \which在代物时常常可以通用,但有时只宜于用that ,不用which.

(1)     先行词是形容词最高级或者它的前面有形容词最高级时

This is the best that has been used against air pollution(反对空气污染) in cities.