第1个回答 2008-04-28
If you want to know,Be patient ,please!
从句只是句子的一个成分，不能独立，从句有自己的主语和谓语等句子成分，通常由关
联词引导。主句是句子的主体。由一个主句和一个或一个以上的从句构成的句子叫做复合句。
依据句法功能，从句可分为：名词性从句、定语从句和状语从句。
名词性从句
名词性从句是在句子中起名词作用的主谓结构，它可以在主从复合句中作主语、宾语、
表语、介词的宾语以及同位语。
1. 主语从句
主语从句可以由连词that, wh-疑问词或名词性关系词引导。
⑴由连词that引导：从句可以位于句首，但常常用形式主语it替代，从句本身则放在
主句后面，如：
That he will come to the party is certain.
It happened that the harvest was bad that year.
Is it true that she has never been there?
通常在口语或非正式文体中，that常可省略，但必须是在用先行词it的情况下，如：
It’s a pity (that) you are leaving.
⑵由wh-疑问词引导：从句既可以前置，又可以借助于先行词it后置。如：
Who cleaned the meeting room is unknown.
It’s still a question when we shall have our sports meet.
It is uncertain whether he will come.
注意：在疑问句中，wh-疑问词所引导的从句不能位于句首，如：
Is it known where she went?
⑶主语从句也可由名词性关系词引导，这类从句只能位于句首，如：
Where she went was Los Angeles.
What will be, will be.
Whomever you invite will be welcome.
2. 宾语从句
⑴宾语从句可用that引导，这时that仅起连接作用，不充当从句中的成分。如果连接词
要在从句中起语法作用，就要使用连接词what等来引导从句。
I believe that he is honest.
We fully understood what he meant.
⑵有些形容词的后面也可跟宾语从句。这类形容词有：certain, afraid, aware, sorry, sure,
worried等。如：
I’m afraid that you are wrong on this point.
I am aware that you have been exceptionally kind to me.
⑶宾语从句也可以用how, when, who, which, where, why等词引出，此时即使主句是一
个疑问句，宾语从句也必须保持陈述句的语序。如：
Go and ask why he was late yesterday.
Can you tell me where the hospital is?
⑷跟在介词后面的宾语从句一般不能由that来引出，只限于except, in, but, besides, save
等五个介词的宾语从句，其它介词后面不能跟由that引出的宾语从句，而只能跟由what, how,
whether等引出的宾语从句。
You are wrong in that you took effect for cause.
I would go with you, except that I have to work that day.
They were arguing about what was to be done.
I’m thinking of whom I should ask for help.
3. 表语从句
表语从句通常由that引出，当然how, why, where, when等也可以引出表语从句。常见的
表语从句有下面两种句型：
⑴"The reason…that"：表示“原因是……”。如：
The reason for leaving was that it was too cold.
⑵"It (This, That) is because…"：表示“这是因为……”，“这是由于……缘故”。如：
This is because iron contains more carbon than steel.
4. 同位语从句
同位语从句表示与之同位的名词中心词的实际内容。
⑴同位语从句起进一步解释说明先行词的作用，通常由that引导。同位语从句的先行词
通常是一些抽象名词，如：appeal, idea, truth, fact, theory, belief, plan, hope, proposal, rumor,
suggestion等。
There is truth in the old saying that necessity is the mother of invention.
⑵由wh-疑问词引导，如：
I have no idea when he will come.
It is difficult to answer your question why I did it.
⑶由名词性关系词引导，如：
Fame and fortune—what others sought after with zest—was all rubbish to him.
⑷注意同位语和that引导的定语从句的区别：that在同位语从句中只起引导从句的作用，
本身并无意义，也不在句子中担当任何成分；而定语从句的that既引导从句又充当句子成分。
The news that he intended to come gave us much pleasure.（同位语从句，that不作句子成
分。）
He is the best speaker that addressed the meeting.（定语从句，that在从句中作宾语，指代
的先行词是主句中的主语。）
定语从句
定语从句是在句子中起形容词作用的主谓结构，通常修饰它前面的名词或代词，即它的
先行词。定语从句是由关系代词和关系副词引导的。
1. 关系代词引导的定语从句
⑴引导定语从句的关系代词有：who, whom, whose, which, that。
⑵关系代词在从句作主语、宾语、定语和表语的作用；当作宾语时，关系代词常常可省
略。如：
This is the girl (whom) you’ve been looking for.
⑶当定语从句所修饰的先行词是人或人格化的动物时，引导词用who, whom或whose；
如果先行词是无生命的东西，用关系代词which；而that可用于以上两种情况。
The man who robbed you has been arrested.
That is the book which cost me twenty dollars.
Which还可以指婴儿、动物和表示单数意义的集合名词，如：
The baby (which) the nurse brought in was Mary’s child.
⑷关系代词that和which的语法区别
当先行词的前面有形容词的最高级修饰时，通常用that而不用which。如：
The final match is one of the most exciting football games that I have ever seen.
当定语从句所修饰的先行词的前面有all, any, little, only, much等修饰时，或者这些先行
词本身就是all, one, little, much, nothing等不定代词时，通常用that而不用which。
I am interested in all that you have told me.
It seems that is the only thing that we can do now.
当定语从句作介词的宾语时，只能使用which而不用that。
The world in which we live is in constant motion and in constant change.
当定语从句是与代词、数词或名词词组连用引导非限定性定语从句时，只能使用which
而不用that。
I bought a dozen eggs, five of which broke when I dropped the box at my door.
当先行词的前面有the + only (first, last, same, next, very)等词修饰时，通常用that而不用
which。
This is the very movie that I want to see.
当被用来指代整个句子，引导非限定性定语从句时，只能使用which而不是that。
Things then improved, which surprises me.
Her brother snatched the letter away, at which she was furious.
2. 关系副词引导的定语从句
⑴引导定语从句的关系副词有：when, where, why, how等。
⑵关系副词when, where, why在从句中作状语时，可用“介词+which”来替代。如：
The reason why (= for which) he is in hospital hasn’t been known yet.
3. 限定性定语从句和非限定性定语从句
限定性定语从句与先行词关系密切，用来描述主句所涉及的人或物的具体情况，与主句
不可分割。这种从句在口语中前后没有停顿，在文字中前后没有逗号。
非限制性定语从句与先行词之间的关系比较松散，为主句所描绘的人或物提供一些附加
情况，并非绝对必要。这种从句在口语中有停顿，在文字中往往用逗号与主语隔开。
另外，非限定性定语从句可用which, who, whose, when, where等来引导，但不可以用that
来引导。如：
The wine, which was in the cellar, was ruined.（非限定性）
The wine which (that) was in the cellar was all ruined.（限定性）
在限定性定语从句中，关系代词有时可省略；但是在非限定性定语从句中，关系代词不
能省略。