今天来给大家分享下高中重要的语法知识—主语从句。主语从句是四大类名词性从句（主语从句、表语从句、宾语从句和同位语从句，名词性从句在复合句中的作用相当于名词。）之一。句子的主语可以由单词（名词、代词等）、名词性短语或句子来充当。当一个句子来充当主语时，我们把这个句子称为主语从句。 主语从句一般放于句首，有时可以放于句末。
根据引导词的不同，可将主语从句分为以下三类。
1.that引导的主语从句：that无词义，只起连接作用；that不作句子成分；一般不省略。
That you will win the gold medal seems unlikely.
你会赢得金牌似乎是不可能的。(你似乎不可能会赢得金牌)
That she survived the accident is a miracle.
她从事故中存活下来是个奇迹。
That he was right was quite clear. 他是对的很清楚。（很清楚，他是对的）
That he was able to come made me very happy. 他能来使我很高兴。
2.whether引导的主语从句：意为“是否”；在从句中不充当任何成分。
Whether we will hold a party tomorrow depends on the weather.
明天我们是否举行聚会取决于天气
Whether he’ll come here isn’t clear. 他是否会来这里还不清楚。
Whether it is true remains a question.它是真是假还是个问题。
3.how/ wh- 疑问词引导的主语从句：每个引导词都有相应的词意；在从句中充当一定的成分。
Why dinosaurs died out remains a puzzle.
恐龙为什么会灭绝仍然是个谜。(why 作原因状语)
Where we’ll go hasn’t been decided.
我们要去哪里还没有定下来。(where 作地点状语)
When we shall have our sports meet is still a question.
我们什么时候开运动会还是个问题。(when作时间状语)
Which kind of food is the best is still not certain.
哪种食物是最好的仍然不确定.(which 作主语)
What you need is more practice.
你需要的(东西)是更多的耐心。（你需要更多的耐心）(what作宾语)
Who will do the job has not been decided.
谁将做这份工作还没被决定。 (who 作主语)
(还没决定谁去做这份工作)
Whose watch was lost is unknown.不知道是谁的表丢了。 (whose 作定语)
Whoever breaks the law should be punished.无
论谁违法都该受到惩罚。 (whoever 作主语)
Whatever she wants is fine with me.
无论她要什么，我都没意见。(whatever 作宾语)
Whichever of you comes here will receive a prize.
你们中无论哪一个来到这里将会得到奖品。(whichever 作主语)
特别注意：
1.疑问词引导主语从句，疑问词本身是什么词意，在从句中也翻译成什么词意，但有时也会有相应的变化。
What I need is more money.
我需要的(东西)是更多的钱。（我需要更多的钱。）
What he is worried about is his final examination.
他担心的(事)是他的期末考试。
2.主语从句一定要用陈述句语序，即主语在谓语之前。
例如以下两个主语从句语序则为错误。
Why did your brother give it up remains a puzzle.
Where will we go hasn’t been decided.
而以下三个主语从句语序就为正确的陈述句语序（主语在前，谓语在后）。
Why your brother gave it up remains a puzzle.
Where we’ll go hasn’t been decided.
Who will do the job has not been decided
3.主从句的谓语动词都要考虑时态：
要根据主从句的意思来选择用相应的时态，主从句动词的时态可能相同也可能不同。
4. no matter who/ what/ which/when ... 不可引导主语从句。
错误句：No matter who comes here will be given a gift.
正确句: Whoever comes here will be given a gift.
5.主语从句一般被认为是单数形式，主句谓语动词应该用单数形式。
Whatever you did is right.
That she survived the accident is a miracle.
What caused the accident remains unknown.
What we need is time.
Who will be our monitor hasn't been decided yet.
6.有时主语从句放在句首，过于长且笨重，出现“头重脚轻”的情况，影响句子结构的平衡，此时常常用it 作形式主语，把主语从句移至句子的末尾。
It is hard to understand why there is gravity.
It is a complete mystery how the prison escaped.
It is a pity that you didn’t attend the lecture yesterday.
It is very important that we must master English words as many as possible.
It hasn’t been decided yet when the new restaurant will open.
以下是几种常见的it 作形式主语的含主语从句的复合句句型。
（1）It is n. that 主语从句：
It’s a pity that my new computer doesn’t work. 很遗憾，我的新电脑坏了。
It’s a shame that you have to leave so soon.很遗憾你这么快就得离开。
It’s a fact that he didn’t steal things from the shop.
事实是他没有偷这个店的东西。
It’s a surprise that Pluto is no longer considered a planet in our solar system.
很惊讶冥王星不再是太阳系中的一个行星。
It’s no doubt that they all come from Australia.
毫无疑问他们都来自澳大利亚。
（2）It is adj. that 主语从句：
→ adj.为important,necessary,interesting,obvious,clear,possible
,impossible,true,well-known,strange,unbelievable等。
It is very important that we should learn English well.
我们应该学好英语，这是很重要的。
It's necessary that we drink enough water every day.
我们每天喝足够多的水是必要的。
It 's well-known that Yao Ming is a great basketball player.
众所周知，姚明是一位很棒的篮球运动员。
It’s clear/obvious that you made the wrong decision.
很清楚/明显有做了错误的决定。
（3）It is done. that 主语从句：
It is said that the professor has succeeded in carrying out this experiment.
据说这位教授成功开展了这项实验。
It is reported that the new underground line has been completed in our city.
据报道我们城市的新地铁线已经竣工。
It is believed that there is no life on the moon.人们相信月球上没有生命。
It has been proved that humans can’t live without air and water.
已经证明没有空气和水人类不能存活。
（4）It is vi. that 主语从句：
It happened that I met my old friend,Jack.碰巧我遇到了我的老朋友，杰克。
It suddenly occurred to me that I have left my keys in my room.
我突然想起我把钥匙落在房间
7.若that引导的主语从句直接位于句首，则that不能省略；若that引导的主语从句位于句末，而在句首使用了形式主语it，则that可以省略：
That you didn’t go to the talk was a pity.
很遗憾你没去听报告。(that不可省)
It was a pity (that) you didn’t go to the talk.
很遗憾你没去听报告。(that可省)
强调句型It is/was...that...与“It is/was n. that主语从句的区别。
→判断方法：还原法。即把It is/was 和that去掉，剩余成分仍能重新构成
一个具有完整意义的句子，则原句就为强调句，否则就不是。例如：
It is the fact that has made us unhappy.
把It is ...that ... 去掉，
剩下the fact has made us unhappy.（这个事实使我们不高兴。）句子意义完整。
所以It is the fact that has made us unhappy. 是强调句。
就是这个事实使我们不高兴。
而句子：It is a fact that he has lost the game.
当把It is...that...去掉后，
剩下 a fact he has lost the game.无法组成一个具有完整意义的句子。
所以It is a fact that he has lost the game. 是含主语从句的复合句。
事实是他已经输了这场比赛。
小结。
对于主语从句的有关知识，今天就分享这些。希望对大家的英语学习有所帮助。也希望大家多多点赞多多关注多多评论，一起探讨学习，共同进步。
巩固练习。
判断是主语从句还是强调句。
It is a pity that you didn’t go to see the film.
It is the fact that has made us unhappy.
It is a fact that he has lost the game.
It was a nice dress that I bought in the supermarket last night.
It was in the supermarket that I bought a nice dress last night.
It’s a surprise that Pluto is no longer considered a planet in our solar system.
单选。
1. _____ some mammals came to live in the sea is not known.
A. Which B. Since C. Although D. How
2. I am sure that _____ she said is wrong.
A. which B. all C. this D. what
3. _____ he saw both surprised and frightened him.
A. That B. When C. What D. Which
4. _____ is warm sunshine.
A. What do we all need. B. What all we need
C. What we need D. What we all need
5. _____ is a pity that he should feel so upset.
A. What B. That C. He D. It
6. _____ book you borrow must be returned within a week.
A. What B. Which C. Whichever D. That’s
7.________ makes mistakes must correct them.
A. What B. That C. Whoever D. Whatever
8.________ the boy didn't take medicine made his mother angry.
A. That B. What C. How D. Which
9.____ we can't get seems better than ____ we have.
A. What, what B. What, that C. That, that D. That, what
10.____ we'll go camping tomorrow depends on the weather.
A. If B. Whether C. That D. Where
11._________is going to do the job will be decided by the Party committee.
A. That B. Why C. How D. Who
12.______the house will be built will be discussed at tomorrow's meeting.
A. If B. Where C. That D. What
12._______you come or not is up to you.
A. What B. If C. Why D. Whether
13._______makes mistakes must correct them.
A. Who B. Anyone C. Whoever D. Anybody
14._______team will win the match is a matter of public concern.
A. Which B. That C. If D. How
