名詞性從句，即指性質相當于名詞的從句，它包括主語從句、賓語從句、表語從句和同位語從句。在句子中起名詞的作用。

在近年的英語考試中，名詞性從句考得最多的是主語從句、賓語從句、表語從句。

主語從句，即在復雜句中充當主語成分的句子。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。

引導主語從句的連詞主要有：
從屬連詞：that whether
連接代詞：who whoever whom whose what whatever which whichever
連接副詞：when where how why

今天和小編一起來看下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)?

好了，以上的這些還請大家務必要掌握，在日常的學習中一定要勤加練習，在具體的句子中加以理解，一切問題就可以迎刃而解了。