主语从句讲解(3)
主语从句的用法。
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来介绍。
一．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
①主语从句常用it作形式主语，一般常用句型为：It is+{名词/形容词/过去分词}+主语从句或It +不及物动词 + that 从句. 例如：
It is still a question whether she will come or not.
It is strange that you should like him.
It is still unknown which team will win the match.
It seems that he has seen the film.
另外，还有一些比较多见的结构：
It turned out that……；
It has been proved that……;
It happened/occurred that……；
It is well-known that……等等
②而强调句则不同，它的结构是：It+be+被强调部分+that+从句
强调主语：It is the times that produce their heroes.时势造英雄
强调宾语：It is English that Professor Lin teaches us.
强调状语：It was in shanghai that I saw the film.
判断是否是强调句有一个方法，就是将that以后的“句子的其余部分”拿出来单独看，看有没有缺成分，缺的是什么成分，再把谓语动词后面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句完整的句子了，那就说明是强调句。
2. 用it 作形式主语的结构
(1) It is +名词+that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+that从句
It is natural that… 很自然…
It is strange that… 奇怪的是…
(3) it +不及物动词+that从句
It seems that… 似乎…
