語法必看：主語從句全面剖析
爲使同學們更好地掌握其用法,本文對主語從句語法做了一個詳細的梳理，幫助大家梳理主語從句的語序，連接詞的選用等內容，對於it構成的主語從句做了詳細的解釋,以便幫助大家掌握這一重要知識點。
一、主語從句的引導詞
主語從句通常由連詞that和whether、連接代詞或連接副詞以及關係代詞型what引導。
1. that引導
That she is still alive is a consolation. 她還活着是使人感到寬慰的。
That she became an artist may have been due to her father's influence. 她成爲畫家可能是受她父親的影響。
That you are coming to London is the best news I have heard this long time. 你將來倫敦是好久以來我聽到的最好消息。
That she was chosen made a tremendous stir in her village. 她被挑選上，在她村子裏引起很大轟動。
2. whether引導
Whether it will do us harm remains to be seen. 是否對我們有害還要看一看。
Whether they would support us was a problem. 他們是否會支持我們還是一個問題。
3. 連接代詞引導
Whoever is top from wins the game when two matched players meet. 兩強相爭勇者勝。
Whichever (of you) comes in first will receive a prize. 無論(你們)誰先到都可以得獎。
Whichever you want is yours. 你要哪個哪個就是你的。
4. 連接副詞引導
When we arrive doesn't matter. 什麼時候到沒有關係。
How it was done was a mystery. 這是怎樣做的是一個謎。
Where I spend my summer is no business of yours. 我在哪裏過暑假不關你的事。
5. 關係代詞型what引導
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。
What's done is done. 事已成定局。
What he says is not important. 他說的話並不重要。
What I am telling you is mere impressions. 我和你說的都不過是一些印象而已。
What make the river more beautiful are the lotus plants growing in the water. 爲河水增色的是水裏的荷花。
What you need is a good-sized canvas bag. 你需要的是一個比較大的帆布袋。
What I am afraid of is their taking him to Portugal. 我擔心的是他們把他帶到葡萄牙去。
What struck me was that they have all suffered a lot. 給我很深印象的是他們都受過很多苦。
二、主語從句與形式主語it
(1) 對於以連詞that引導的主語從句，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重要。
It is essential that a meeting be convened this week. 本週開一次會非常重要。
It is appropriate that this tax be abolished. 廢除這個稅是恰當的。
It's unfair that so many people should lose their jobs. 竟有這麼多人失業這是不公平的。
(2) 對於以連接代詞(副詞)引導的主語從句，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) 對關係代詞型what引導的主語從句，通常直接將主語從句放在句首。如：
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. 他是什麼意思很清楚。
(4) 如果句子是疑問句，則必須用帶形式主語it的結構：
How is it that you are late again? 你怎麼又遲到了？
