定语从句

关系代词有who, whom, whose, which, that, as,和关系副词when, where, why。

（1）that指物时一般可与which互换，但在下列情况下，要用that而不用which。

a. 先行词有all, everything等不定代词时，如，

Everything (that) he did is wrong.

b. 先行词被all, every, no, some, any, little, much等修饰时，如，

I'll read all the books (that) you lend me.

c. 先行词被序数词或形容词最高级修饰时，

This is the first letter (that) the boy has written.

d. 先行词被the only, the very, the same, the last修饰时，如

He is the very man (that) I'm looking for.

e. 只用which的情况

在介词后或在非限定性定语从句中

This is the book about which we have talked a lot.

The book, which he gave me yesterday, is very interesting.

f. where和when作关系副词

This is the room where I worked.

This is the room which I stayed in.

I remembered the day when we lived there.

I remembered the day that I spent there.

g. as和which

as 可以放于句首，而which 不可以

As you know, he is good at English.

three of them 和three of which

I have a lot of books, three of which are in Russian.

I have a lot of books and three of them are in Russian.

（2. ）“介词+关系代词”的情况：

在固定短语中介词不能提前；判断介词的口诀：瞻前顾后看意义

瞻前——看先行词；顾后——找从句动词；看意义——看全句表达含义

(3. )先行词在从句中充当地点状语时，关系词用where 或者介词加which；先行词在从句中充当时间状语时，关系词用when或者介词加which；先行词在从句中充当原因状语时，关系词用why或者for which。

(4. )注意as和which在非限制性定语从句中代表主句所表达的内容的区别：

位置不同：as从句放在主句前或后均可；而which从句只能放在主句后

作用不同：as从句动词常常是see know等，因而相当于插入语；which从句则在陈述一件事实。