ii. it作为形式主语

it作为形式主语，无具体意义，真正的主语由动名词、动词不定式和主语从句担任，被后置。

It is difficult to climb a mountain.

爬山是很艰难的。

正常形式：To climb a mountain is difficult.

It is a good habit to do morning exercises.

做早操是个好习惯。

It's important to study English.

学习英语很重要。

It is dangerous playing with fire.

玩火是危险的。

It is no use learning without thinking.

学而不思则罔。

It is wrong arguing with your parents.

和你的父母吵架是错误的。

常见句型有：

1. It is necessary (important, easy, difficult, natural, common, interesting, pleasant ...) for sb. to do sth./that ...

It is very important for us to learn English well .

对我们来说学好英语很重要。

2. It is kind (clever, brave, careful, careless, foolish, honest, nice, polite ...) of sb. to do sth.

It is very kind of you to say so . = You are very kind to say so.

你真好这样说。

3. It is no good (useless, no use, a waste of time) doing sth.

It's no use crying over spilt milk.

牛奶一洒哭也没用。

It's no harm drinking running water in that area.

在那个地区喝自来水没有害处。

4. It is a pity (a shame) that ...（should）....(主语从句表示出乎预料)

It is pity that you didn't see that good film.

你没看到那部好电影真可惜。

It is a shame that he didn't pass the exam.

他没有通过考试，真丢人。

5. It is said （reported, believed, thought, announce, estimated) that ...

It is said that he will be late today.

据说他今天会来晚。

6. It is suggested (advised, ordered, requested ...) that ... (should) ... (主语从句用虚拟语气表达)

It is suggested that the meeting (should) be put off.

有人建议推迟会议。

It was ordered that we (should) arrive there in two hours.

命令要求我们两小时内到那里。

7. It takes sb. +一段时间+ to do sth.

It took thousands of people many years to build the Great Wall.

建长城花了千百万人很多年时间。

It will take him three hours to go to Hangzhou by train.

乘火车去杭州要花他三小时的时间。

8. It seems (appears, happens, turns out, occurred to sb.) that ...

It seems that no one knows anything about the matter.

似乎没一个人知道有关此事的任何情况。

It seemed that things were not as they expected.

似乎情况不像我们预料的那样。

It appears to me that the report must be true.

在我看来这个报告肯定是真的。

9. It matters/doesn't matter whether ...

It doesn't matter what you say.

你说什么不要紧。

Does it matter if he can't finish the job in time?

如果他不能按时完成这项工作，关系重大吗？

10. It is uncertain whether ...

It is uncertain whether he's coming.

还不能肯定他是否能来。

11. It is necessary (important, natural, strange ...) that ... (should) ... (主语从句用虚拟语气)

It is necessary that he (should) remember these words.

他很有必要记住这些话。

12. It is no wonder/an honour that ...

He missed the first bus, so it is no wonder that he was late for the meeting.

他误了第一班车，因此难怪他开会迟到了。

专项练习

1. _______ is a fact that Global Warming has had influenced human beings' life.

A. There

B. This

C. That

D. It

2. It is wrong _______ treat your mother like that.

A. that you to

B. of you to

C. for you to

D. because you

3. Is _______ necessary to complete the task before National Day?

A. this

B. that

C. it

D. he

4. Does _______ matter if he can't finish the job on time?

A. this

B. that

C. he

D. it

5. He hasn't had any food for two days. _______ that he is so hungry.

A. There is no point

B. There is no need

C. It is no wonder

D. It is no way

6. _______ he has been fired because of his absence for a long time with no reason.

A. It is said that

B. They all said that

C. That is announced that

D. It was reported

7. It is no use _______ books without reading.

A. to buy

B. in buying

C. of buying

D. buying

8. _______ human beings can live on the moon in the next twenty years.

A. There seems impossible

B. This is impossible for

C. It is impossible of

D. It seems impossible that

9. _______ in the school regulation that students should wear school uniforms at school.

A. What is required

B. What requires

C. It is required

D. It requires

10. —How do you know him well?

—_______ that we live in the same neighborhood.

A. It is

B. That is

C. It is because

D. It happens

答案速查　1-5　DBCDC　6—10　ADDCD