例如：That you will win the medal seems unlikely.
That you are so indifferent bothers me.
That she survived the accident is a miracle.
2、用連接代詞或連接副詞if, whether 引導的主語從句。
例如： Which of them escaped from the prison is still a mystery.
When they will come hasn』t been made pubic.
Whether she is coming or not doesn』t matter too much.
例如：What you need is more practice.
What I want to know is this. 我想知道的就是這事。
Whatever we do is to serve the people.
例如：That light travels in straight lines is known to all.
=It is known to all that light travels in straight lines.
When the plane is to take off has not been announced .
= It has not been announced when the plane is to take off.
錯:It is a book what he wants.
對:What he wants is a book. 他想要的是本書。
例如：Has it been settled who will be sent to carry out the task ?
1、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.
It is common knowledge that the whale is not a fish.
It is no surprise that Bob should have won the game.
2、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.
It is doubtful whether she will be able to come.
It was really astonishing that he refused to talk to you .
It is essential that he should be here by the weekend .
It seems obvious that we can not go on like this.
3、It is +過去分詞+從句
It is said that … 據說……
It is reported that … 據報道……
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.
It is estimated that the vase is 2000 years old.
It is used to be thought that a new star must be due to a collision between two stars.
It has not been made clear when the new road is to be opened to traffic.
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.
It now appears that they are in urgent need of help.
It does not matter if I missed my train, because there is another later.
It happened that I saw him yesterday.
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.
It does not interest me whether you go or not.
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係。
It does not make any difference whether it rains or not .
It does not make the least difference to me what you do.
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麼重要影響嗎？
 英語網 http://www.etmeet.com/Article/bk/high/ges/200701/19064.html
 百度知道 http://zhidao.baidu.com/question/23072602.html 學英語報社 http://www.e-l-e.net.cn/jiaoyan/jxzhidao/jxlilun/200809/17438.htm