★ 主语从句

一、概念

在复合句中作主语的从句叫主语从句。主语从句通常由从属连词that，whether和连接代词what，who，which，whatever，whoever以及连接副词how，when，where，why等词引导。that在句中无词义，只起连接作用;连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。

如：What he wants to tell us is not clear.

It is known to us how he became a writer.

Where the English evening will be held has not yet been announced.

二、由that/whether引导的主语从句

⒈ 由连词that引导的主语从句：引导词that无含义，在句中不做成分，不可以省。

如：That you will win the medal seems unlikely.

That you are so indifferent bothers me.

That she survived the accident is a miracle.

⒉ 用连词 whether 引导的主语从句：whether有含义(是否)，在句中不做成分，不可以省。

如：Whether she is coming or not doesn't matter too much.

备注：It doesn't matter if 是固定句型。

三、用连接代词引导的主语从句

⒈ 在由连接代词who, whose, whom, which, what, whoever, whomever, whichever, whatever引导的名词性从句中，其连接代词在句中起名词性作用，担当一定成分，有意义。

如：What you need is more practice?

What I want to know is this?

Whatever we do is to serve the people.

⒉ whatever, whoever, whichever引导的主语从句的区分：

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Whatever 相当于anything that , 是 what 的强调形式，表示“无论什么”。

如：Whatever she does right.

Whoever相当于anyone who,是who 的强调形式，表示“无论谁，任何…的人”。

如：Whoever walks around in such a heavy rain will catch a cold.

Whichever“无论哪个，无论哪些”，既可以指人，也可以指物，可以单独使用，可以修饰名词，也可以后跟of短语。

如：Whichever book you borrow doesn't matter to us.

四、用连接副词引导的名词性从句

连接副词when, where, why, how引导的主语从句中，其=连接副词有含义，在句中作状语。

如：Where we should leave it is a problem.

When they will come hasn’t been made pubic.

五、it 形式主语的情况

有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末，但是不能代替由what引导的主语从句。主语从句后的谓语动词一般用单数形式。常用句型如下：

⑴ It + be + 名词 + that从句

⑵ It + be + 形容词 + that从句

⑶ It + be + 动词的过去分词 + that从句

⑷ It + 不及物动词 + that 从句

另注意在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do”，常用的句型有：

It is necessary (important, natural, strange, etc.) that…

It is a pity (a shame, no wonder, etc.) that…

It is suggested (requested, proposed, desired, etc.) that…