定語從句

關系代詞有who, whom, whose, which, that, as,和關系副詞when, where, why。

（1）that指物時一般可與which互換，但在下列情況下，要用that而不用which。

a. 先行詞有all, everything等不定代詞時，如，

Everything (that) he did is wrong.

b. 先行詞被all, every, no, some, any, little, much等修飾時，如，

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

c. 先行詞被序數詞或形容詞最高級修飾時，

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

d. 先行詞被the only, the very, the same, the last修飾時，如

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

e. 只用which的情況

在介詞后或在非限定性定語從句中

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作關系副詞

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. ）“介詞+關系代詞”的情況：

在固定短語中介詞不能提前；判斷介詞的口訣：瞻前顧后看意義

瞻前——看先行詞；顧后——找從句動詞；看意義——看全句表達含義

(3. )先行詞在從句中充當地點狀語時，關系詞用where 或者介詞加which；先行詞在從句中充當時間狀語時，關系詞用when或者介詞加which；先行詞在從句中充當原因狀語時，關系詞用why或者for which。

(4. )注意as和which在非限制性定語從句中代表主句所表達的內容的區別：

位置不同：as從句放在主句前或后均可；而which從句只能放在主句后

作用不同：as從句動詞常常是see know等，因而相當于插入語；which從句則在陳述一件事實。