(1/5) 名词性从句-主语从句简介
作句子主语的从句叫主语从句，主语从句通常由that，whether，what，who，which，whatever，whoever，以及how，when，where，why等词引导。
(2/5) that引导的主语从句
that 引导主语从句时，that 没有意义，但不能省略(that 引导宾语从句时可以省略)。
例句：
It worried her a bit that her hair was turning gray.
她的头发正在变白，这使她很不安。
此处that引导的主语从句，it作形式主语，that 不能省略。
That she is a rich woman is known to us all.
我们都知道，她是个富有的女人。
这是that 引导的主语从句，that 不能省略。这句话可以改为用it 作形式主语的句型：It is known to us all that she is a rich woman.
We didn’t know (that) you had sold your house.
我们不知道你已经把你的房子卖了。
这是that引导的宾语从句，that 可以省略。
(3/5) whether引导的主语从句
whether 既可以引导主语从句也可以引导宾语从句，但if一般不能引导主语从句；whether 后面可以加or not, 而if 一般不与or not 连用。
例句：
Whether or not she'll come isn't clear.
她是否来还不清楚。
此处whether引导主语从句。
It all depends on whether we can get their cooperation.
这完全取决于我们是否能得到他们的合作。
此处whether 引导的是宾语从句，作介词on 的宾语。
(4/5) what引导主语从句
what的意思是“所……的事/物”, 相当于the thing(s) that…, that which… 或those which…。
例句：
What she saw frightened her.
她看到的事情吓了她一跳。
What was once regarded as impossible has now become a reality.
曾经被认为不可能的事情，现在已经变成了事实。
What hurt our feelings most was the personal comment of the judge.
最伤我们感情的是法官的私下评论。
What is gone is gone.
过去的事就过去了。
(5/5) it 做形式主语
当主语从句处在句首时，有时谓语结构比较短，会形成头重脚轻的句式，不符合英语语言规则，因此可以将主语从句用it替代，而真正的主语从句置于句尾。常见的四种情况是：
（1）It is+名词+主语从句；
eg：It is a pity that you should have to leave.
It is still a mystery what caused the accident.
（2）It is+形容词+主语从句；
eg：It is clear that the whole project is due to failure.
It is certain that he will win the match.
如果是It is necessary /important /strange /natural+that引导的主语从句，从句中的谓语动词一定要用should+动词原形；
eg：It is necessary that one should master the skills of operating computer.
It is important that we all should attend the meeting.
It is strange that the man should have stuck to his silly ideas.
(3) It is+过去分词（said /planed/expected/known） +主语从句；
eg：It is said that President Bush will visit our school next week.
It is known to all that the gun powder was first invented by the Chinese.
It is suggested that the work should be done with great care.
(4) It +系动词+形容词表语形式+主语从句
eg：It seemed certain that he will win the prize.
It happened that the two cheats were there.
免责声明：以上内容源自网络，版权归原作者所有，如有侵犯您的原创版权请告知，我们将尽快删除相关内容。
