摘要：進入高三總復習的第一階段，同學們應從基礎知識抓起，扎扎實實，一步一個腳印地過“英語知識點”關。復習時，將高三英語必背知識點熟練掌握運用，小編相信您一定可以提高英語成績!

一.主語從句

主語從句是在復合句中充當主語的從句，通常放在主句謂語動詞之前或由形式主語it代替，而本身放在句子末尾。

1. It 作形式主語和it引導強調句的比較。

It 作形式主語代替主語從句，主要是為了平衡句子結構，主語從句的連接詞沒有變化。而it引導的強調句則是對句子某一部分進行強調，無論強調的是什么成分，都可用連詞that。被強調部分指人是也可用who/whom。

例如：

It is a pity that you didn’t go to see the film.

It doesn’t interest me whether you succeed or not.

It is in the morning that the murder took place.

It is John that broke the window.

2. 用it 作形式主語的結構。

(1) It is +名詞+從句

It is a fact that … 事實是…

It is an honor that …非常榮幸

It is common knowledge that …是常識

(2) it is +形容詞+從句

It is natural that… 很自然…

It is strange that… 奇怪的是…

(3) it is +不及物動詞+從句

It seems that… 似乎…

It happened that… 碰巧…

(4) it +過去分詞+從句

It is reported that… 據(jù)報道…

It has been proved that… 已證實…

3. 主語從句不可位于句首的五種情況。

(1) if 引導的主語從句不可居于復合句句首。

(2) It is said ， (reported) …結構中的主語從句不可提前。

例如：

It is said that President Jingo will visit our school next week. (right)

That President Jiang will visit our school next week is said. (wrong)

(3) It happens…， It occurs… 結構中的主語從句不可提前。

例如：

It occurred to him that he failed in the examination. (right)

That he failed in the examination occurred to him. (wrong)

(4) It doesn’t matter how/whether …結構中的主語從句不可提前。

例如：

It doesn’t matter whether he is wrong or not. (right)

Whether he is wrong or not doesn’t matter. (wrong)

(5) 含主語從句的復合句是疑問句時，主語從句不可提前。

例如：

Is it likely that it will rain in the evening? (right)

Is that will rain in the evening likely? (wrong)

4. What 與that 在引導主語從句時的區(qū)別。

What 引導主語從句時在句時在從句中充當句子成分，如主語.賓語.表語，而that 則不然。

例如：

1) What you said yesterday is right.

2) That she is still alive is a consolation.

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