介绍一下主语从句和表语从句？？

主语从句和表语从句和宾语从句大同小异，统称名词性从句。
主语从句(Subject Clause)
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.
（2）Whether we will go for an outing tomorrow remains unknown.
（3）Who will be our monitor hasn't been decided yet.
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.
表语从句 用作表语的从句叫作表语从句，它位于主句中的连系动词之后。引导表语从句的词有从属连词that、whether、as though(if)；关系代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等；关系副词when, where, why, how, however, whenever, wherever等。可以接表语从句的连系动词由be, look, remain, seem等。That引导表语从句时，在口语中，间或可以省略。The trouble is that we are short of money. 困难是我们资金短缺。That is why stone walls are used instead of fences around New England fields.这就是为什么在新英格兰用石头墙而不用栅栏的原因。At that time, it seemed as if I couldn't think of the right word anyhow.当时,我似乎怎么也想不出一个恰当的字眼来。 仔细研读，有问题再问。Ok

个人分数

表语从句和主从都是名词性从句，简单地说如果在be动词后的表语一般是由名词或形容词来充当，如果是一个句子的话，那么这个句子就是表从，同理，主语由句子来充当的那就是主从，名词性从句就是有位置和成分来判断的

表语从句定义：在一个复合句中，从句作的是主语的表语成分。在复合句中充当主语成分的句子叫做主语从句.