which在定从中怎么用

2.which指物，在定语从句中作主语或宾语。例如：

A dictionary is a book which gives the meaning of words. Here is the book(which) he bought yesterday.

定语从句是用一个句子来作定语修饰名词或代词，通常放在它所修饰的名词或代词之后，这种名词或代词叫做先行词。引导定词从句的关联词为关系代词(which , that, who, whom, whose, as)和关系副词(when ,where ,why )，关系代词在定语从句中可用作主语，宾语，定语等，关系副词在定语从句中只是用作状语。eg：
(1) The student(先行词) who answered the question(主语) was John.
(2)I know the reason(先行词) why he was so angry(状语).

定语从句在选择关连词that 与which时，常常容易出错，所以应记住什么时候只能用that，什么时候只能用which.
（1）．只能用 that 的情况归纳4种：即先行词被序数词最高级修饰过；先行词为all 、everything、nothing等不定代词；先行词同时是人和物并列时；最后先行词分别被the only 、the very the same、the last 修饰。请看下列四组例句，注意其先行词：
①．The first thing that we should do is to work out a plan .
②．I t almost seemed as if the good man were trying to teach us all that he knew at this lesson .
③．This is the very dictionary that I want to find .
（2）．只用which 情况有两种情况：一是非限制性定语从句，关连词要用which；二是做介词宾语时只能用which。请看下列两组例句：
I said