一、主语从句的概念与类型

主语从句在复合句中作主句的主语，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.

注意: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 + adj. / n. +从句

It is a pity/shame that...遗憾的是……

It is possible that...很可能……

It is unlikely that...不可能……

2)It +不及物动词+从句

It seems/appears that...似乎……

It happened that...碰巧……

3)It + be +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:

It is believed that at least a score of buildings were damaged or destroyed.据信，至少有二十座楼房遭到破坏或彻底毁掉.

It is suggested that the meeting should be put off.有人建议会议延期召开.

It is known to all that Taiwan is an inseparable part of China.众所周知，台湾是中国不可分割的一部分.

[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

A. There B. This C. That D. It

二、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 is done can't be undone.

(谚语)已成定局，无可挽回.

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 we should work out a plan to deal with the present serious situation is important.

我们应该制定一项计划来应付目前严峻的形势，这一点非常重要.

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

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引导动词后的宾语从句时一般可通用，但介词后的宾语从句、主语从句(放在句首时)、表语从句常由whether引导.

例如:

Whether she will go home or not is unknown.

她是否回家还不得而知.

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.

[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

[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

-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

三、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

四、以it作形式主语的主语从句与强调句型的区别

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.

Key: 1-5 DBDBA 6-10 ACBDB 11-15 AAADB