作者：邢新
it用法有很多，一起来看一下。
一、可指代前文提到过的事物或事情。例如：
My book is missing. I can't find it anywhere. 我的书不见了，我到处都找不到它。
You have saved my life. I will never forget it. 你救了我的命，我永远不会忘记这件事。
Her mother just died. It's a terrible shock to her. 她的母亲刚去世，这对她是个极大的打击。
Jack is ill. Have you heard about it? 杰克生病了。你听说了吗？
二、用以代替指示代词this, that。例如：
-Who is that? 那是谁？
-It's my friend. 是我的朋友。
-What is this? 这是什么？
-It's a frog. 是只青蛙。
三、用于表示天气、时间、距离等。例如：
It's cloudy / very cold today. 今天多云 / 很冷。
It's half past nine now. 现在是九点半。
It's a long way to the post office. 这儿离邮局很远。
四、在附加疑问句中，可以用来代替all, everything等不定代词。例如：
All is going well, isn't it? 一切顺利，不是吗？
Nothing could make her change her views, could it? 没什么能使她改变观点，是吗？
Everything is prepared well, isn't it? 一切都准备好了，不是吗？
五、可以在句中作形式主语或形式宾语，代替由不定式、动名词或从句表示的真正的主语或宾语。例如：
It is very difficult to finish the task in such a short time. 在如此短的时间内完成任务很困难。
I found it impossible to get there on time. 我发现按时到那儿是不可能的。
It is said that he refuses to come. 据说他拒绝来。
It is no use learning these figures by heart. 记住这些数字没有用。
六、可用于含有before或since的特定句型中。例如：
It was not long before the war broke out. 不久战争就爆发了。
It is five months since I smoked. 我已有5个月不吸烟了。
七、 可用在强调结构中，用来强调句子的某一成分（通常是主语、宾语或状语）。在这种结构中，it 不可用this或that替代。例如：
It was last summer that I graduated from the university. 我是去年夏天从那所大学毕业的。
It was at an evening party that I first saw her. 我第一次见到她是在一次晚会上。
It is Professor Wu that / who sent me the letter. 给我寄信的是吴教授。
It is this novel that they talked about last week. 他们上周讨论的就是这部小说。