主語從句的用法
一個句子在復合句中充當一個主語，那么這個句子就是主語從句。下面學習啦小編就給大家介紹主語從句的用法。
主語從句的用法
主語從句 定義:在句子中擔當主語的是一個從句,這個從句就叫做主語從句。
主語從句是在復合句中充當主語的從句，通常放在主句謂語動詞之前或由形式主語it代替，而本身放在句子末尾。
1. It 作形式主語和it引導強調(diào)句的比較
It 作形式主語代替主語從句，主要是為了平衡句子結構，主語從句的連接詞沒有變化。而it引導的強調(diào)句則是對句子某一部分進行強調(diào)，無論強調(diào)的是什么成分，都可用連詞that。被強調(diào)部分指人是也可用who/whom。例如：
It is a pity that you didn’t go to see the film.
It is +名詞+從句
It is a fact that… 事實是……
It is good news that … ……是好消息
It is a question that … ……是個問題
It is common knowledge that … ……是常識
類似的名詞還有：a pity;a wonder;a good thing; no wonder; surprise等。
例如：It is a mystery to me how it all happened.
這一切是怎么發(fā)生的是個謎。
It is common knowledge that the whale is not a fish.
鯨魚不是魚，這是常識。
It is no surprise that Bob should have won the game.
鮑勃會贏得這場比賽，這不足為奇。
It is +形容詞+從句
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……
類似的形容詞還有：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.
很明顯導體和絕緣體在工業(yè)中都很重要。
It is doubtful whether she will be able to come.
她是否能來令人懷疑。
It was really astonishing that he refused to talk to you .
他拒絕和你說話真是令人驚訝。
It is essential that he should be here by the weekend .
周末之前，他應該到這里是必要的。
It seems obvious that we can not go on like this.
很明顯我們不能這樣下去了。
It is +過去分詞+從句[1]
It is said that … 據(jù)說……
It is reported that … 據(jù)報道……
It has been proved that … 已證明……
It must be proved that… 必須指出……
類似的過去分詞還有：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.
大家都認為他是最好的選手。
It is estimated that the vase is 2000 years old.
據(jù)估計這個花瓶有2000年的歷史。
It is used to be thought that a new star must be due to a collision between two stars.
過去一直認為新星是由于兩顆星星之間碰撞產(chǎn)生的。
It has not been made clear when the new road is to be opened to traffic.
還沒弄清楚這條路將開始通車。
It +不及物動詞+從句
It seems that … 好像是……
It happened that… 碰巧……
It follows that … 由此可見……
It has turned out that … 結果是……
類似的不及物動詞還有：seem, appear, occur, follow, happen, turn out, etc.
例如：It turned out that nobody remembered the address.
結果是無人記得那個地址。
It now appears that they are in urgent need of help.
看起來他們急需幫助。
It does not matter if I missed my train, because there is another later.
沒有趕上這趟火車沒有關系，稍晚還有一趟。
It happened that I saw him yesterday.
碰巧我昨天看見他了。
當“及物動詞 + 賓語”較短時，也可用這種結構。
例如：It shocked me that Peter did not tell anybody where he was.
讓我吃驚的是彼得沒有告訴任何人他在哪里。
It does not interest me whether you go or not.
我對你去不去不感興趣。
It +某些固定結構+ 主語從句。
例如：It doesn’t make too much difference (It doesn’t make any difference / It doesn’t alter the situation)，whether it rains or not . 下不下雨都沒有多大關系。
It does not make any difference whether it rains or not .
下不下雨沒什么分別。
It does not make the least difference to me what you do.
對我來說你做什么都無關緊要。
Is it of much consequence to you that Mr. Wang has failed to do it ? 王先生沒有做成這件事對你有什么重要影響嗎?
主語擱置句末
(1)It is certain that he will win the match.
(2)It is true that he has made a very important discovery in chemistry.
(3)It is very likely that they will hold a meeting.
(4)It is strange that he should do that.
(5)It is important that we all should attend the meeting.
(6)It is strange that the man should have stuck to his silly ideas.
(7)It is a pity that we won't be able to go to the south to spend our summer vacation.
(8)It is still a mystery what caused the accident.
(9)It is said that he has gone to shanghai.(=He is said to have gone to shanghai)
(10)It is known to all that the gun powder was first invented by the Chinese.
(11)It is suggested that the work should be done with great care.
(12)It seems that he has seen the film.(=He seems to have seen the film)
(13)It happened that the two cheats were there. (=The two cheats happened to be there)
小結:
(1)以that 引出的主語從句,常以形式主語it引導. It is +形容詞/名詞/某些動詞ed + that 從句.
(2) 在有些that從句中要用虛擬語氣 (should+do/should+have done)例句4,5,6,11.
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主語從句的用法
