1.it作形式主语

(1)真实主语是动词不定式。

It is difficult to translate this article．

翻译这篇文章很难。

It is getting harder every day for a lazy man to get a living．

懒汉谋生是日益困难了。

The man whose business it is to look after the children is not here．

负责照看孩子的那个人不在这儿。

提示：

这个句子也可表达为The man whose business is to look after the children is not here．

不过此时动词不定式就不再是主语了，而是表语。(参见动词不定式)

(2)真实主语是动名词。

It is no use going there so early．

这么早去那里没有用。

It has been a great honor your coming to visit me．

你的来访是我很大的荣幸。

(3)真实主语是主语从句。

It is strange that he did not come at all．

真奇怪，他竟还没来。

It doesn't matter what you do．

你做什么都没关系。

It hasn't been decided which flight they will take．

还没有决定他们乘哪个航班。