I．要点
根据从句在句中的句法功能，从句可分为名词性从句、定语从句和状语从句。
1、 名词性从句
（1） 主语从句
What he wants is a piece of paper.
It is believed that he can solve the problem.
注：主语从句的谓语动词用单数。
（2）宾语从句
I don''t know how to solve the problem.
Do you know where he lives?
（3）表语从句
The problem is who can help me.
This is why I came here.
（4）同位语从句
I have no idea where he went.
I heard the news that he would come.
同位语从句用that引导，常跟在fact, idea, news, promise, thought, message, hope, belief, doubt等词后，that在从句中不作任何成分。
2、定语从句
在复合句中，修饰某一名词或代词，或修饰整个主句的从句叫做定语从句，引导定语从句的关系代词有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.
3、状语从句
在复合句中起状语作用的从句叫做状语从句。状语从句可分为时间状语、地点状语、原因状语、目的状语、结果状语、条件状语、行为方式状语、比较状语、让步状语等多种。
II． 例题
例1、 _______ I accept the gift or refuse it is none of your business.
A. If B. Whether C. Even if D. No matter when
解析：该题答案为B。whether可以和or连用，if不可以，此外if一般仅用于宾语从句。
例2、The way _______ these comrades look at problems is wrong.
A. where B. in that C.X D. with which
解析：该题答案为C，先行词是way，定语从句中用that或 in which来引导或不填。
例3， ____a long time since I saw you last time.
A．It was B. It is C. It had been D. It can be
解析：该题答案为B，It is +时间数+ since引导的从句是一个句型，意为"从…时候以来过了多久了。"
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