主语从句
一 定义:在句子中担当主语的是一个从句,这个从句就叫做主语从句。
通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。
Why he refused to work with you is still mystery.
他为什么拒绝和你一起工作，仍不得其解。
Whoever comes is welcome.
不论谁来，都是受欢迎的。
二 引导主语从句的词有从属连词that, whether以及连接代词who, what, which, whoever,
whatever, whichever和连接副词when, where, why, how等.例如:
That she was chosen made us very happy.她当选了使我们很高兴.
What caused the accident is a complete mystery.是什么导致了这次事故还完全是一个
谜.
Whether she will come or not is still a question.她是否来还是一个问题.
Which team will win the match is still unknown.哪个队会赢得这场比赛还不知道.
Whoever comes to the party will receive a present.参加聚会的每一个人都将收到一份
礼物.
When they will start has not been decided yet.他们何时出发还没决定.
三 上述例句中的主语从句都是放在句首,但有时为了使句子结构平衡,避免\"头重脚轻\常用it作形式主语,而把从句放在后面.例如:
It is a pity that she has made such a mistake.她犯了这样一个错误,真是遗憾.
It depends on the climate whether they are going shopping today.他们是否今天去购物还得看天气情况.
这样就构成了下面一些常用句型:
（1） It is +名词+从句
It is a fact that… 事实是……
It is a pity/shame that...遗憾的是……
类似的名词还有：a wonder；a good thing； no wonder； surprise等。
例如：It is a mystery to me how it all happened.
这一切是怎么发生的是个谜。
It is no surprise that Bob should have won the game.
鲍勃会赢得这场比赛，这不足为奇。
（2） It is +形容词+从句
It is necessary that … 有必要……
It is clear that … 很清楚……
It is likely that … 很可能……
It is important that … 重要的是……
It is possible that...很可能……
类似的形容词还gt有：strange; natural; obvious; true; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising;
interesting; astonishing, etc. 例如：
It is obvious that conductors and insulators are both important in industry.
很明显导体和绝缘体在工业中都很重要。
It is doubtful whether she will be able to come.
她是否能来令人怀疑。
It was really astonishing that he refused to talk to you .
他拒绝和你说话真是令人惊讶。
It is essential that he should be here by the weekend .
周末之前，他应该到这里是必要的。
It seems obvious that we can not go on like this.
很明显我们不能这样下去了。
（3） It is +过去分词+从句
It is said that...据说……
It is known to all that...众所周知……
It is reported that...据报道……
It is believed that...据信……;人们相信……
It is suggested that...有人建议……
It must be pointed out that...必须指出……
It has been proved that...已证明…….例如:
类似的过去分词还有：estimated; expected; thought; hoped; noted; discussed;
required; decided; suggested; demanded; made clear; found out,etc.
例如：It is thought that he is the best player.
大家都认为他是最好的选手。
It is estimated that the vase is 2000 years old.
据估计这个花瓶有2000年的历史。
It is used to be thought that a new star must be due to a collision between
two stars.
过去一直认为新星是由于两颗星星之间碰撞产生的。
It has not been made clear when the new road is to be opened to traffic.
还没弄清楚这条路将开始通车。
（4） It +不及物动词+从句
It seems/appears that...似乎……
It happened that...碰巧……
It has turned out that … 结果是……
类似的不及物动词还有：seem, appear, occur, follow, happen, turn out, etc.
例如：It turned out that nobody remembered the address.
结果是无人记得那个地址。
It now appears that they are in urgent need of help.
看起来他们急需帮助。
It happened that I saw him yesterday.
碰巧我昨天看见他了。
[巩固练习]
1. Does _______ matter if he can't finish the job on time?
A. this B. that C. he D. it
2. It worried her a bit _______ her hair was turning grey.
A. which B. that C. if D. for
3. _______ is a fact that English is being accepted as an international language.
A. There B. This C. That D. It
四 学习主语从句应该注意的几个问题
1 引导词that与what
what既有引导主语从句的作用,同时又在从句中作句子成分(主语、宾语、表语等).这时what相当于all that/everything that...,常译成\"所……的(东西、事情、话等.)\";
而that只起连接作用,本身无实际意义,在从句中也不担当任何句子成分.但that引导的主语从句放在句首时,不能省略that.例如:
What we can't get seems better than what we have.我们得不到的东西似乎比已得到的要好.
That a new teacher will come to teach us geography is true.一位新老师将来教我们地理,这是真的.
[巩固练习]
4. _______ what they told me really true?
A. Has B. Is C. Does D. Have
5. It matters little _______ a man dies, but _______ matters much is _______ he lives.
A. how; what; how B. how; it; how C. why; it; why D. that; what; that
6. _______ she couldn't understand was _______ fewer and fewer students showed interest in her lessons.
A. What; why B. That; what C. What; because D. Why; that
7. It is pretty well understood _______ controls the flow of carbon dioxide in
and out the atmosphere today.
A. that B. when C. what D. how
8. _______ fashion differs from country to country may reflect the cultural differences from one aspect.
A. What B. That C. This D. Which
9. -What made her parents so angry?
- _______ she had failed in the examination.
A. As B. Because C. Since D. That
2 引导词if和whether
if和whether在引导位于句首的主语从句时，只能选用whether.如：
Whether we shall raise ducks or geese remains to be decided.我们是养鸭还是养鹅仍没决定.
=It remains to be decided whether/if we shall raise ducks or geese.
但我们不能说If we shall raise ducks or geese remains to be decided.
[巩固练习]
10. _______ we'll go camping tomorrow depends on the weather.
A. If B. Whether C. That D. Where
3 其它引导词
连接代词who, which, whom, whose有各自的意义,起连接作用,并在从句中充当语、宾语、表语、定语等;连接副词when,where, why, how等有各自的意义,起连接作用,并在从句中充当状语.
[巩固练习]
11. -Do you remember _______ he came?
-Yes, I do. He came by car.
A. how B. when C. that D. if
12. It was a matter of _______ would take the position.
A. who B. whose C. whom D. whomever
13. -I drove to Zhuhai for the air show last week.
-Is that _______ you had a few days off?
A. why B. when C. what D. where
14. I read about it in some book or other, does it matter _______ it was?
A. where B. what C. how D. which
4 以it作形式主语的主语从句与强调句型的区别
\"It be + adj./n. + that-clause\"与强调句型均有It be...that...之类的语言标志,但不同的是:①前者中的that从句是主语从句.若删掉其中的It be和that,则剩余部分不论结构还是语意都不能成为一个句子;但若将后者中的It be和that去掉,则剩余部分的结构和语意仍能构成一个完整的句子.②强调句型译为汉语时可加上\"正是……\"或\"就是……\"之类的字眼,而主语从句则不可以.请比较下面两个句子:
It is surprising that Mary should have won first place.令人惊奇的是玛莉竟然获得了第一名.
It is Mary that has won first place.正是玛莉得了第一名.
第一句话中的It是形式主语,that引导的是主语从句.句中的It is和that无法删除,一旦删除句子就不成立.
第二句是强调句型,其中的It is和that可以去掉,因为没有It is和that句子仍然很通顺.
5 语气
在It is necessary / natural / important / strange...+ that-clause这类句型里,that所引导的主语从句中谓语动词用\"should +原形\表虚似语气.例如:
It is necessary that the problem should be settled at once.这个问题必须马上解决.
It's strange that he should have gone away without telling us.他竟然没向我们说一声就走了,真是奇怪.
[巩固练习]
15. It is necessary that a college student _______ at least a foreign language.
A. masters B. should master C. mastered D. will master
Key: 1-5 DBDBA 6-10 ACBDB 11-15 AAADB
6 必背
用形式主语it引导的主语从句相当多，有些已形成固定的语法和译法。常见的有：
It is said that... 据说…… It is reported that... 据报导……
It is well known that... 众所周知…… It is announced that... 据宣布……
It is believed that... 人们相信…… It is thought that... 人们认为……
It is understood that... 自不待言…… It must be pointed out that... 必须指出……
It must be admitted that... 必须承认……
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