涉及it用法的五类常考内容如下：

一、考查 it 用作形式主语的用法

当不定式、动名词、从句等用作主语时，为避免头重脚轻，通常在句首使用形式主语it，而把真正的主语放在句子末尾。如：

It's no good sitting up too late. 熬夜没有好处。

It is quite clear that he has read the book. 很显然，他读过这本书。

It doesn't matter what he says. 他说什么没关系。

【特别提醒】注意it用作形式主语的三类特殊句式：

1.用作动词look, seem, appear, happen, occur, follow等的主语(后接that从句或as if从句)。如：

It seems that he knows everything. 他好像什么都知道。

It (so) happened that I had no money with me. 碰巧我没带钱。

2.当系表结构后接有if 或when引出的状语从句时，通常在系表结构前使用形式主语表示说话人对某情况的看法。如：

It was a great surprise to me when he did a thing like that. 他这样做使我很吃惊。

It would be a tragedy if anything went wrong. 如果出了什么事就是一个悲剧。

3.用于if it were not for… / if it hadn't been for…(若不是因为)。如：

If it hadn't been for the freezing wind they could have reached the injured man in time. 要不是有刺骨的寒风，他们就及时赶到伤员身边了。

二、考查 it 用作形式宾语的用法

当不定式、动名词、从句等用作宾语且其后跟有宾语补足语时，就应在宾语补足语前使用形式宾语，而将真正的宾语移至句末：

We found it difficult to persuade her. 我们发现很难说服她。

He makes it a rule to get up before dawn. 他习惯于天亮前起床。

I think it very strange that he goes out walking almost every night. 我认为他几乎每晚都出去散步是很奇怪的。

【特别提醒】注意it用作形式宾语的三类特殊句式：

1. 动词+it+if / when从句

当enjoy, like, dislike, love, hate, prefer, appreciate等动词后需要接一个if或when引导的从句时，此时必须要先在动词后接it作形式宾语。如：

She won't like it if you arrive late. 她不喜欢你迟到。

He hates it when people use his bike. 他讨厌别人用他的自行车。

I'd prefer it if I didn't have to do so much work. 要是我不必做那么多工作，那就太好了。

I would appreciate it very much if you would help me with it. 如果你能帮助我做这事，我会十分感激。

2. 动词+介词+it+that从句

能用于此句型的主要有三个动词，即depend on, answer for, see to。如：

You may depend on it that he will turn up in time. 你可以相信他会及时赶到的。

I can't answer for it that the boy is honest. 我不能保证这个男孩是诚实的。

I'll see to it that all these letters will be sent to the post before twelve. 我将注意让所有的信件在12点以前送到邮局。