二、主語從句與形式主語it

有時為了考慮句子平衡，通常在主語從句處使用形式主語it，而將真正的主語從句移至句末。這分三種情況：

(1) 對于以連詞that引導(dǎo)的主語從句，通常用形式主語代主語從句：

It's a pity that he didn't come.
很遺憾他沒來。

It is important that he should know about this. 他必須知道此事。

It's vital that we be present. 我們出席是至關(guān)重要的。

It was intended that you be the candidate. 大家的意圖是讓你當候選人。

It is important that this mission not fail. 這項使命不失敗至關(guān)重要。

It is essential that a meeting be convened this week. 本周開一次會非常重要。

It is appropriate that this tax be abolished. 廢除這個稅是恰當?shù)摹?/P>

It's unfair that so many people should lose their jobs.
竟有這么多人失業(yè)這是不公平的。

It's amazing that she should have said nothing about it.她竟未談及此事令人驚訝。

It's unthinkable that they should deny my request.
他們竟然拒絕我的請求，這是不可思議的。

That they should refuse to sign the petition required great courage.
他們拒絕在請愿書上簽字這是需要很大勇氣的。

(2) 對于以連接代詞(副詞)引導(dǎo)的主語從句，可以使用形式主語代主語從句，也可直接在句首使用主語從句：

Whether they would support us was a problem. 他們是否會支持我們還是一個問題。

It was a problem whether they would support us. 他們是否會支持我們還是一個問題。

It remains to be seen whether it will do us harm or good.
它對我們是利是害，還得看看再說。

(3) 對關(guān)系代詞型what引導(dǎo)的主語從句，通常直接將主語從句放在句首。如：

What we need is money. 我們需要的是錢。

What I want to know is this. 我想知道的就是這一點。

有時也可將助用形式主語。如：

It is clear enough what he meant. 他是什么意思很清楚。

(4) 如果句子是疑問句，則必須用帶形式主語it的結(jié)構(gòu)：

Is it true that he is the girl's father? 他是那女孩的父親，是真的嗎？

How is it that you are late again? 你怎么又遲到了？

三、連詞that的省略問題

引導(dǎo)主語從句的連詞that 有時可省，有時不能省，其原則是：若that引導(dǎo)的主語從句直接位于句首，則that不能省略；若that引導(dǎo)的主語從句位于句末，而在句首使用了形式主語it，則that可以省略：

That you didn't go to the talk was a pity. 很遺憾你沒去聽報告。(that不可省)

It was a pity (that) you didn't go to the talk. 很遺憾你沒去聽報告。(that可省)