1、主语从句：作句子主语的从句叫主语从句。
①
主语从句通常由下列词引导：
1）从属连词whether 等；
2）连接代词what，who，which，whatever，whoever，whom 等；
3) 连接副词how，when，where，why 等。
连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。注：whom、who指人，what指物，whatever，whoever表示泛指意义。例如：
What he wants to tell us is not clear. 他要跟我们说什么，还不清楚。
Who will win the match is still unknown. 谁能赢得这场比赛还不得而知。
ow he became a writer is known to us . 我们都知道他是如何成为一名作家的。
Where the English evening will be held has not yet been announced. 英语晚会将在哪里举行，还没有宣布。
__________ Barbara Jones offers to her fans is honesty and happiness.
A. Which
B. What
C. That
D. Whom
The villagers have already known ______ we’ll do is to rebuild the bridge.
A. this
B. that
C. what
D. which
some people regard as a drawback（缺点） is seen as a plus by many others.
A. Whether
B. What
C. That
D. How
is known to us all is that the 2008 Olympic Games will take place in Beijing.
A.It
B.What
C.As
D.Which
was most important to her, she told me, was her family.
A.It
B.This
C.What
D.As
matters most in learning English is enough practice.
A.What
B.Why
C.Where
D.Which
parents say and do has a life-long effect on their children.
A.That
B.Which
C.What
D.As
What we used to think
impossible now does seem possible.
A.is
B.was
C.has been
D.will be
makes this shop different is that it offers more personal services.
A.What
B.Who
C.Whatever
D.Whoever
The shopkeeper did not want to sell for
he thought was not enough.
A.where
B.how
C.what
D.which
_____ made the school proud was _____ more than 90% of the students had been admitted to key universities.
A. What; because
B. What; that
C. That; what
D. That’ because
2、that在句中无词义，只起连接作用；It is +adj./ v-ed/ v-ing+that +完整句子.
主语从句
It is obvious to the students ______ they should get well prepared for their future.
A. as
B. which
C. whether
D. that
_______fashion differs from country to country may reflect the cultural differences from one aspect.
What B. That C. This D. Which
主语从句中It 作形式主语：
注意：有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下：
（1）It + be + 名词 + that从句：It is a fact that
事实是
It is an honor that 非常荣幸
It is common knowledge that
…是常识
It is a pity that
遗憾……
（2）It + be + 动词的过去分词+ that从句:
It is said that
据说
It is reported that 据报道
It has been proved that 已经证明
It is believed that …
人们认为
It is supposed that…
据猜测
（3）It + 不及物动词（vi） + that 从句：
It seems that
似乎
It happened that 碰巧
It appears that
似乎
（4）It + be + 形容词 + that从句
It is natural that…
很自然…
It is strange that…
奇怪的是…
注意:在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do”，常用的句型有：
It is necessary (important, natural, strange, etc.) that …
It is suggested (requested, proposed, desired, etc.) that…
当人作主语时，表语用sure或certain, 但在句型It is certain that…中，不可用sure替代certain。
It was never clear _______ the man hadn’t reported the accident sooner.
A. that
B. how
C. when
D. why
It is still under discussion __________the old bus station should be replaced with a modern hotel or not.
A. whether
B. when
C. which
D. where
Before a problem can be solved, it must be obvious ______the problem itself is.
A. what
B. that
C. which
D. why
It is uncertain
side effect the medicine will bring about, although about two thousand patients have taken it.
A. that
B. what
C. how
D. whether
It is none of your business
other people think about you.Believe yourself.
A.how
B.what
C.which
D.when
worries me the way he keeps changing his mind.
A.This
B.That
C.What
D.It
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
4、It 作形式主语和it引导强调句的比较
①It 作形式主语代替主语从句，主要是为了平衡句子结构，主语从句的连接词没有变化。
②it引导的强调句则是对句子某一部分进行强调，无论强调的是什么成分，都可用连词that引导，被强调部分指人时也可用who/whom。例如：
a) It is a pity that you didn’t go to see the film.
你不去看那场电影真可惜。
b) It doesn’t interest me whether you succeed or not. 我对你成功与否不感兴趣。
c) It is in the morning that the murder took place. 谋杀案是在早上发生的。（强调句型）
d) It is John that broke the window. 是John打碎的窗户。（强调句型）
注意：since, if 不能引导主语从句，但当it做形式主语，主语从句放在句末时，if, whether均可
5、主语从句不可位于句首的五种情况：
（1）if 引导的主语从句不可居于复合句句首。
（2）It is said /reported…结构中的主语从句不可提前。例如：
正确表达：It is said that President Jiang will visit our school next week.
错误表达：That President Jiang will visit our school next week is said.
（3）It happens/occurs…结构中的主语从句不可提前。例如：
正确表达：It occurred to him that he failed in the examination.
错误表达：That he failed in the examination occurred to him.
（4）It doesn’t matter how/whether …结构中的主语从句不可提前。例如：
正确表达：It doesn’t matter whether he is wrong or not.
错误表达：Whether he is wrong or not doesn’t matter.
（5）含主语从句的复合句是疑问句时，主语从句不可提前。例如：
正确表达：Is it likely that it will rain in the evening?
错误表达：Is that will rain in the evening likely?
6、what 与that 在引导主语从句时的区别
what 引导主语从句时在句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如：
a) What you said yesterday is right.
b) That she is still alive is a consolation
【疑难点击】
1．由what, whatever, whoever等引导的主语从句，必须置于谓语动词之前，不能用it作形式主语。
Whatever was said here must be kept secret.
Whoever breaks the law will be punished.
She is very dear to us. We have been prepared to do
it takes to save her life.
A. whichever
B. however
C. whatever
D. whoever
team wins on Saturday will go through to the national championships.
A.No matter what
B.No matter which
C.Whatever
D.Whichever
2. 由which, when, where, whether等引导的主语从句，可置于谓语动词前，也可用it作形式主语。但如果是疑问句，就只能用it作形式主语。
Whether he'll come or not makes no difference.＝It does't make any difference whether he'll come or not.
Hasn't it been decided yet when and where we'll hold the sports meet?
1 ______ he will come is certain.
A What
B That
C Which
D As
2 ______ we need is more time.
A What B that C Why D Which
3 It is a pity ______ he can’t attend our meeting.
A what B that C which D As
4 It's hard to say ______ football team will win the match.
A what B which C why D that
5 _____ he did it is not known.
A Why B Which C What D That
6 My idea is ______ we should help her do housework.
A that B what C why D which
7 The question is _____ we can catch the early bus.
A if B whether C why D what
8 This is _____ he wanted.
A what B which C where D why
9 This is ______ she had a day off. A what B why C which D how
10 I think _______ it is necessary for her to finish the task.
A that B what C which D who
11 Hearing ______ her son was badly wounded, she hurried to the hospital.
A what B that C which D why
12 Our teacher suggested ______ we should try to make changes.
A what B that C which D why 13 Please tell me _____ is the first man to invent a car. A what B which C why D who
14 Show me ______ bus I should take to the city center.
A what B which C why D who
15 I don’t know ______old they are.
A what B how C why D who
16 The news _____China hosted the 2008 Olympic Games successfully is very encouraging.
A that B how C why D who
17 His absence due to the fact ______ he was seriously ill.
A how B which C that D what
18 The suggestion _______ we think it in another way raised a storm of objections.
A what B which C that D why
19 The idea ______ we should help the people in the earthquake-stricken areas is worth praising.
A that B what C why D how
0 He made a promise ______ anyone set him free he would make him very rich.
A that what B if C what D that if
三． 填空题 来填空。 用 what, how, which, when, where, why, whether 来填空。 1 _____ she will leave for Guangzhou is not known.
2 ______ I am going to say has nothing to do with music.
3 ______ one she will choose doesn’t matter much.
4 ______ they were carrying out the experiment has not been decided yet.
5 ______ Kevin is late for the concert is not clear.
6 ______ she will study medicine or computer needs to be discussed.