引导主语从句连词有that,whether,who,what,whatever等定义:如果一个句子在复合句中充当一个主语,那么这个句子就是主语从句.
第一部分：常规主语从句，即句子在复合句中充当一个主语
（1）That he finished writing the composition in such a short time surprised me.
（2）Whether we will go for an outing tomorrow remains unknown. （3）Who will be our monitor has't been decided yet.
（4）Whom we must study for is a question of great importance. （5）What caused the accident remains unknown.
（6）Whatever you did is right.
（7）Whose watch was lost is unknown.
（8）What we need is time.
（9）What we need are good doctors.
小结:
（1)引导主语从句连词有that,whether,who,what,whatever等
（2)连词位于句首不能省略
（3)主语从句大多数情况下视为单三,但也有例外,如例9
第二部分：为了防止句子头重脚轻，通常把形式主语it放在主语位置，真正主语搁置于句末
（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 vacation.
（8）It is still a mystery what caused the accident.
（9）It is said that he has gone to Taiwan.(=He is said to have gone to Taiwan)
（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)
小结:
（1)以that 引出的主语从句,常以形式主语it引导. It is +形容词/名词/某些动词ed + that 从句.
（2) 在有些that从句中要用虚拟语气(should+do/should+have done)例句4,5,6,11.
名词性从句
在句子中起名词作用的句子叫名词从句(Noun Clauses）。名词从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。
一、引导名词性从句的连接词
引导名词性从句的连接词可分为三类：
连词：that（无任何词意）
whether, if均表示“是否”表明从句内容的不确定性）
as if ,as though（均表示“好像”，“似乎”）
以上在从句中均不充当任何成分
连接代词：what, whatever, who, whoever, whom,
whose, which. whichever, whomever
连接副词：when, where, how, why
不可省略的连词：
1. 介词后的连词
2. 引导主语从句和同位语从句的连词不可省略。
That she was chosen made us very happy.
We heard the news that our team had won.
比较：
whether与if 均为"是否"的意思。但在下列情况下，whether 不能被if 取代：
1. whether引导主语从句并在句首
2. 引导表语从句
3. whether从句作介词宾语
4. 从句后有"or not"
Whether he will come is not clear.
大部分连接词引导的主语从句都可以置于句末，用it充当形式主语。
It is not important who will go.
It is still unknown which team will win the match.
二.主语从句
1. 作句子主语的从句叫主语从句。主语从句通常由从属连词that，whether，if和连接代词what，who，which，whatever，whoever以及连接副词how，
