主语从句有哪些?包括哪些从句?有哪些连接词连接?做什么成分?连接哪些词性的词?

定义:在复合句中充当主语的句子叫做主语从句.第一部分：常规主语从句,即句子在复合句中充当一个主语 主语从句的时态：不受主句的时态影响和限制.（1）That he finished writing the composition in such a short time surprised us all.（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 What we need are good doctors.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.（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 （1）It is strange that he should do that.（2）It is important that we all should attend the meeting.（3）It is strange that the man should have stuck to his silly ideas.（4）It is suggested that the work should be done with great care.主语从句与宾语从句两者的用法和在句中的作用是不同的,下面从它们的各自用法,介绍：一．主语从句 主语从句 定义:在句子中担当主语的是一个从句,这个从句就叫做主语从句.主语从句是在复合句中充当主语的从句,通常放在主句谓语动词之前或由形式主语it代替,而本身放在句子末尾.1.It 作形式主语和it引导 强调句 的比较 It 作形式主语代替主语从句,主要是为了平衡句子结构,主语从句的连接词没有变化.而it引导的强调句则是对句子某一部分进行强调,无论强调的是什么成分,都可用连词that.被强调部分指人是也可用who/whom.例如：It is a pity that you didn’t go to see the film.2.用it 作形式主语的结构 (1) It is ＋名词＋从句 It is a fact that … 事实是… It is an honor that …非常荣幸 It is common knowledge that …是常识 (2) it is ＋形容词＋从句 It is natural that… 很自然… It is strange that… 奇怪的是… (3) it ＋不及物动词＋从句 It seems that… 似乎… It happened that… 碰巧… (4) it is＋过去 分词 ＋从句 It is reported that… 据报道… It has been proved that… 已证实… 3.主语从句不可位于句首的五种情况 (1) if 引导的主语从句不可居于复合句句首.(2) It is said ,(reported) …结构中的主语从句不可提前.例如：It is said that President Jingo will visit our school next week.(3) It happens…,It occurs… 结构中的主语从句不可提前.例如：It occurred to him that he failed in the examination.(4) It doesn’t matter how/whether …结构中的主语从句不可提前.例如：It doesn’t matter whether he is wrong or not.(5) 含主语从句的复合句是疑问句时,主语从句不可提前.例如：Is it likely that it will rain in the evening?4.What 与that 在引导主语从句时的区别 What 引导主语从句时在从句中充当 句子成分 ,如主语．宾语．表语,而that 则不然.例如：What you said yesterday is right.