名詞性從句：主語從句的語法大全
導語：從句 是復句中具有分屬地位的分句，它是一種絕大部分語言都有的語法結構。下面小編為您收集整理了，希望對您有幫助!
知識要點：
名詞性從句包括：主語從句、表語從句、賓語從句和同位語從句。引導名詞性從句的連詞有：
A.連詞：that, whether, if(這三個詞都不作從句的成分，同時，that無含義，而whether和if都表“是否”)
B.疑問代詞：who, whom, whose, what, which
C.疑問副詞：when, where, why, how
主語從句：在復合句中充當主語的`從句。
1.that引導主語從句
that引導主語從句時不同于其他的連詞，既無詞義也不作成分，只起單純的連接作用，且通常不可以省。為了強調that引導的主語從句而置之于句首時，that不可省。
�、賂hat the driver could not control his car was obvious.
�、赥hat she was chosen made us very happy.
③That he will come is certain.
�、躎hat he would take the risk is true.
�、軹hat he should have married her isn't surprising.
通常，that引導主語從句時用it做形式主語，把從句置于句尾，此時that有時可省。例如：
�、買t was obvious that the driver could not control his car.
�、贗t made us very happy that she was chosen.
③It is certain that he will come.
�、躀t is true that he would take the risk.
⑤It isn't surprising (that) he should have married her.
如果以that從句為主語的句子是疑問句，就只能用先行詞it結構。例如：
�、買s it certain that he will come?
②Is it true that he would take the risk?
it做形式主語有以下幾種不同的`結構：
(1)It + be + 形容詞+ that-從句
�、買t is likely that he will come.
�、贗t is strange that she has ever trusted him.
�、跧t is important that he (should) attend the meeting.
�、躀t is best that he (should) go.
此句型在表示驚訝、喜悅、遺憾等感情色彩時，that從句中的謂語動詞也常用 (should) + v原形。
It is strange that no one should have objected to the plan.
(2)It + be +名詞+ that-從句
It is common knowledge that the whale is not a fish.
It's a pity that he should have catched the train.
(3) It + be + -ed分詞 + that從句
It is said that he is a famous writer.
It is reported that there will be a storm this afternoon.
在表示建議、要求、命令等意義的被動結構中，that從句中的謂語動詞常用(should) do。(參見虛擬語氣部分)
It is suggested that the meeting (should) be held this afternoon.
It is demanded that he (should) leave at once.
(4) It + seem/happen/appear等不及物動詞 + that從句。(look不接that從句，它接to be結構或形容詞)
It seems that he is wrong.
It appears that they are in urgent need of help.
He looks (to be) surprised/happy/sad.
2. whether引導主語從句，意為“是否”，只起連接作用，不充當任何成分。(置于句首時必須用whether引導，置于句尾時，間或可用if。)
Whether he will win the game is not clear.
Whether he will come is uncertain.
Whether she comes or not doesn't concern me.
It is not clear whether/if he will come.
It was uncertain whether he would come.
3. 連詞代詞what, who, which, whose等引導的主語從句。這些連接代詞作用相當于代詞，在從句中擔當主語、賓語、表語、定語等。
What we need is more time.
Who was responsible for the accident is not yet clear.
Whose book it is not important.
Which school you want to go matters much.
4.連接副詞when, where,why, how引導的主語從句。這些連接副詞相當于副詞，在從句中充當狀語。
Why he did this is not known.
When he will come is still unknown.
It is not known why he did this.
How he succeeded is unknown to us.
Where we should hold the meeting needs to be discussed.
注意：wh-引導的主語從句也常用it作形式主語。
5.也可用whatever,whoever,whomever,whenever,wherever等詞引導主語從句，表示“無論什么”、“無論誰”、“無論何時”、“無論在(到)哪里”等。
Whoever told you to give up smoking was quite right.
Whatever he gave you should be handed in.
Whoever told you that was lying.
Whoever comes is welcome.
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