主语从句
一、概述：在句子中起名词作用的各种从句统称为名词性从句。根据它们在句中的语法作用，这类从句又可分为主语从句、同位语从句、表语从句和宾语从句。
二.主语从句主要有三类：
（1） 由连词that引导的主语从句:引导词that无含义,在句中不做成分,不可以省。
例如：That you will win the medal seems unlikely.
你想获得奖牌看起来是不可能的。
That you are so indifferent bothers me.
你如此冷淡使我很烦恼。
That she survived the accident is a miracle.
她在事故中幸免于难简直是奇迹。
（2） 用连词 whether 引导的主语从句:whether有含义(是否),在句中不做成分,不可以省。
例如：Whether she is coming or not doesn’t matter too much.
她来不来都无关紧要。
（3） 用连接代词引导的主语从句(在由连接代词who, whose, whom, which, what, whoever, whomever, whichever, whatever引导的名词性从句中，其连接代词在句中起名词性作用，担当一定成分).
例如：What you need is more practice.
你所需要的是更多的训练。
What I want to know is this. 我想知道的就是这事。
Whatever we do is to serve the people.
我们无论做什么都是为人民服务。
（4）用连接副词when, where, why, how引导的名词性从句(其连接副词有含义,在句中作状语。)
eg:Where we should leave it is a problem.
When they will come hasn’t been made pubic.
他们什么时候来还不知道。
三.注意点:
1.it 做形式主语,而将主语从句放在句末（尤其是当谓语较短时）。
例如：That light travels in straight lines is known to all.
光沿直线传播，这是众所周知的事。
=It is known to all that light travels in straight lines.
众所周知光沿直线传播。
When the plane is to take off has not been announced .
飞机何时起飞还没有宣布。
= It has not been announced when the plane is to take off.
还没有宣布飞机何时起飞。
(当what引导的主语从句表示“…的东西”时，一般不用it作形式主语。)
错:It is a book what he wants.
对:What he wants is a book. 他想要的是本书。
例如：Has it been settled who will be sent to carry out the task ?
谁将被派去执行这项任务决定了吗 ？
固定用法和译法
（1） It is +名词+从句
It is a fact that… 事实是……
It is good news that … ……是好消息
It is a question that … ……是个问题
It is common knowledge that … ……是常识
类似的名词还有：a pity；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 common knowledge that the whale is not a fish.
鲸鱼不是鱼，这是常识。
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……
类似的形容词还有：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 reported that … 据报道……
It has been proved that … 已证明……
It must be proved that… 必须指出……
类似的过去分词还有：known; estimated; expected; believed; 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。
It does not matter if I missed my train, because there is another later.
没有赶上这趟火车没有关系，稍晚还有一趟。
It happened that I saw him yesterday.
碰巧我昨天看见他了。
当“及物动词 + 宾语”较短时，也可用这种结构。
例如：It shocked me that Peter did not tell anybody where he was.
让我吃惊的是彼得没有告诉任何人他在哪里。
It does not interest me whether you go or not.
我对你去不去不感兴趣。
2.只用whether不用if引导主语从句.
Ⅰ．选择题：
1. _____ as much as one-fifth of all timber harvested is not used.
A. The estimate B. The estimate
C. They are estimated D. It is estimated that
2. _____ some mammals came to live in the sea is not known.
A. Which B. Since C. Although D. How
3. _____ we have achieved is attributed to the guidance of our parents.
A. Whoever B. Whatever C. However D. That
4. _____ wealthy does not necessarily mean that a man is greedy.
A. For the reason that he is B. Just because he is
C. The reason of being D. That he is
5. Although _____ happened in this developed country sounds like science fiction, it could occur elsewhere in the world.
A. which B. what C. how D. it
6. _____ she had forgotten to take her notebook.
A. That occurred to her B. She occurred that
C. To her that occurred D. It occurred to her that
7. I am sure that _____ she said is wrong.
A. which B. all C. this D. what
8. We lost our way in the forest, and _____ made matters worse was that it was getting dark.
A. that B. which C. it D. what
9. _____ some mammals came to live in the sea is not known.
A. Which B. Since C. Although D. How
10. _____ or not is still uncertain.
A. He’s coming B. If he is coming
C. That coming D. Whether he’s coming
11. It’s _____ he’ll be able to come.
A. doubt whether B. doubtful C. doubt it D. doubtful whether
12. _____ he is at work in the heart of the big city or at home in the quiet suburb, Dick’s life is tied to machines.
A. Whether B. Till C. If D. Unless
13. _____ he saw both surprised and frightened him.
A. That B. When C. What D. Which
14. _____ is a spell of warm sunshine.
A. What do we all need. B. What all we need
C. What we need D. What we all need
15. _____ is a pity that he should feel so upset.
A. What B. That C. He D. It
16. _____ a spoonful of soil can tell us so much about the structure and early history of the moon.
A. Remarkable B. Quite remarkably
C. It is remarkable that D. It is remarkable fact that
17. _____ you nominate will be elected.
A. Who B. Whom C. Whomever D. That’s
18. _____ book you borrow must be returned within a week.
A. What B. Which C. Whichever D. That’s
19. _____ of us gets home first starts cooking.
A. Who B. Which C. Whichever D. Anyone
20. _____orders he gives are obeyed.
A. Whichever B. Which C. Whatever D. What
