由一个主句和一个或一个以上的从句构成的句子叫复合句。名词性从句在复合句中起名词的作用，它包括主语从句、宾语从句、表语从句，同位语从句四大类，在句中分别用作主语、宾语、表语和同位语。

一、引导名词性从句的关联词

二、主语从句

在复合句中充当主语的从句叫作主语从句。

A.为了强调主语从句的内容，可将从句置于句首。

That you are leaving is a pity. 你要走，真遗憾。

What matters is how you live. 重要的是你如何生活。

Where he lives is not clear. 他住哪儿不清楚。

Who will stay makes no difference. 谁留下来都一样。

Whether the football game will be played depends on the weather.

足球比赛是否举行将视天气而定。

点津坊

连词that引导的主语从句位于句首时，that不可以省略，附加疑问句

用it。

That he has lost his watch is not true, is it?

他手表丢了不是真的，是吗？

B.大部分主语从句都可以用it作形式主语

为了保持句子平衡，主语从句常用it作形式主语，将主语从句后置。用it作形式主语的主语从句结构有如下几种：

1.It is+名词+that从句

Its a pity that we cant go. 很遗憾我们不能去。

It is a fact that English is being accepted as an international language. 英语正在被人们接受为一种国际语言，这是一个事实。

It is no wonder that he is not hungry; he has been eating sweets all day. 难怪他不饿，他整天在吃糖果。

2.It is+形容词+that从句

It is certain that she will do well in her exam.

毫无疑问她考试成绩会很好。

It is probable that he told her everything.

很可能他把一切都告诉她了。

Is it true that the scientist will give us a lecture next week?

下周那位科学家将给我们作报告是真的吗？

比 较

It is reported that there was a fire in the supermarket last night.

据报道超市昨晚失火了。(主语从句)

As is reported, there was a fire in the supermarket last night.

据报道超市昨晚失火了。(定语从句)

3.It+动词+that从句

It seems that Alice is not coming to the party at all.

看起来艾丽丝根本不会来参加晚会。

It happened that I was out that day.

碰巧我那天外出了。 (=I happened to be out that day.)

4.It is+过去分词+that从句

It is said that Mr. Green has arrived in Beijing.

据说格林先生已经到了北京。

It is reported that China has sent another man-made earth satellite into orbit. 据报道中国又成功地发射了一颗人造地球卫星。

5.其他情况

It doesnt matter whether she will come or not.

她是否来这无关紧要。

It makes no difference where we shall have the meeting.

我们在哪里开会毫无区别。

It suddenly occurred to her that she had forgotten to lock the door.

她突然想到她忘记锁门了。……