1. 以what等连接代词引导的主语从句

What you need is more practice. 你需要的是更多的练习。

Whoever wants it may have it. 谁要都可以给他。

同类的连接代词还有：What, who, whom, whose, which, whatever, whoever, whichever

2. 以that, whether从属连词引导的主语从句

It was strange that he had made a mistake. 真奇怪，他竟然错了。

That we need more equipment is quite obvious. 我们需要更多的设备，这是很明显的。

Whether he will join us won't make too much difference.

他是否加入我们，没有太大的差别。

3. 主语从句的引导词that什么时候可以省略

当主语从句不太长时，引导词“that”可以省略

It's clear (that) he has done his best. 很明显他已经尽力而为了。

It's a wonder (that) he didn't fail. 真奇怪，他没有失败。

4. 以when等连接副词引导的主语从句

When they will come hasn't been made public. 他们什么时候来还没有公布。

Where she has gone is not known yet. 她去了哪儿，还不知道。

Why he did it will remain a puzzle for ever. 为什么他做那件事将永远是个谜团。

5. 虚拟语气：主语从句

形容词为necessary, important, impossible, strange, natural, essential时，在“It + be + 形容词或过去分词 + 主语从句”中，主语从句要虚拟。

It is necessary that the problem (should) be discussed at once.

立刻讨论这个问题很有必要。

It is strange that he (should) have so many friends. 太奇怪了，他有那么多的朋友。

6. 主语从句与强调句的区别

注意事项：

1). 在主语从句中，把It was … that去掉之后，就已经完全不像一个句子了。

2). 在强调句中，把It was … that去掉之后，还基本上像个句子。

3). 主语从句有以下的引导词：what, who, whom, whose, which, whatever, whoever, whichever

4). 强调句的引导词只有：that, who。

主语从句：

It was strange that he had made a mistake. 如果把，It was … that 去掉以后，剩下strange he had made a mistake.就不算是句子了。

It is immaterial where or when he goes. 他去何处或者何时去是无关紧要的。

<><>It is said that…, 和It is reported that…这样的结构，后面接的是主语从句：

It is said that he’s got married. 听说他已经结婚了。

强调句：

It was she that had been wrong. 错的是她。（强调主语）如果把，It was … that 去掉以后，剩下she had been wrong.还勉强算的上是一个句子。

It was this novel that they talked about last night. 他们昨晚谈论的是这部小说。（强调宾语）

It was in London that I first saw her. 我是在伦敦第一次见到她的。（强调地点状语）