I 人称it
人称it可以用来代替一个名词、一个短语、一个分句或一个句子，避免它们在句中重复。
1.人称it可以指事物、动植物或性别不明的婴儿。
This is a new dictionary. I bought it yesterday.
There is an old tree in front of his house. It is very tall.
The cat is too lazy to move. I must give it a push.
The Whites have a new baby. It’s lovely.
2.人称it可以指包括许多成员在内的集体。
The Women’s Volleyball Team came back yesterday. It has just won the world championship.
3.人称it可以指一个动作或一件事情。
I like hiking, but he doesn’t like it.
My brother was knocked down by a car, but he survived the accident. It was a narrow escape.
It should never happen again. She left away and left the bicycle unlocked.
4.用在“It is/was +表语”结构中，指明某人或某物的身份的，具有这种作用的it可以用来代替this或that。(有语法学家称其为指示it。)
-Who’s there? -It’s me / the postman / John.
Last night I tripped over something and fell. What’s that? It’s a stone.
II 无人称it
无人称it是虚词，没有任何具体的意义。
1. 无人称it作主语，用于表示自然现象、时间、距离、环境状况等句子中。
It rains / snows / clears up.
It was summer.
It is ten o’clock.
It’s time to go.
How far is it to Tien An Men?
It’s within a stone’s throw.
It’s very quiet.
2. 无人称it用在以seem, appear, happen, turn out 作谓语，后面跟that从句的句子中作主语。
It appears that she is an experienced teacher.
It happened that he had been hurt.
It turns out that his article is very instructive.
It seems that he is always correct.
(上一句可以改成He seems to be always correct. 但不可以说 That he is always correct seems.)
3. 无人称it作主语用于一些被动结构中。
It is said that the new road will be opened to traffic next week.
It is well known that the bridge will be completed ahead of time.
It is considered that the experiment is not worth trying.
4. 无人称it作主语用于一些习惯用语中。
It makes no difference at all. 一点关系也没有。
It’s hard to say. 这很难说。
It comes to nothing. 没有什么结果。
It’s splendid ! 好极了！
III 先行it
先行it也是一个虚词，在句中作形式主语或宾语。
1. 作主语
1) 真正主语是不定式短语。
It is impossible for me to get there the day after tomorrow.
It’s up to you to decide.
2) 真正主语是动名词。
It’s no use trying to persuade him.
It’s no good your doing that over and over again.
3) 真正主语是名词性从句。
It is a pity that he is not coming at all.
It is doubtful whether he would play the part.
It doesn’t matter what you do.
2. 作宾语
用在“S + Vt + it + Co + O”句型中，这种句型中宾语较长而宾语补足语又较短，因此常用it作形式宾语而把真正的宾语放在宾语补足语的后面。
1）真正宾语是不定式短语。
I consider it better to be early.
2) 真正宾语是动名词。
I don’t think it worthwhile taking so much trouble to do the job.
3) 真正宾语是名词性从句。
I think it a pity that we shall never have such a chance again.
IV 强调it
强调it也没有任何具体意义，强调it的句子结构是：
It + is/was + 被强调的成分 + that + 原句的剩余部分
被强调的成分通常是主语、宾语或状语，强调由人所作的主语时，常用who替代that，所有的强调句均可以还原成陈述句。
I met Tom in the zoo yesterday.
→ It was I who met Tom in the zoo yesterday.
→ It was Tom that I met in the zoo yesterday.
→ It was in the zoo that I met Tom yesterday.
→ It was yesterday that I met Tom in the zoo.
练 习
I 指出下列各句it的类型 (A-人称 B-无人称 C-先行 D-强调)
is your daughter who has made that mistake.
appears that he is intelligent.
seems that we are mistaken.
is good for us to go out for a walk every evening after supper.
5.I think it strange that he made so many mistakes in the paper.
is cold outside.
7.(What is it?) It is a ship near the horizon.
was with great difficulty that the mountaineers reached the summit.
was a warm summer morning.
10.(The train pulled in.) It was on time.
11.(I like fish.) It is goog to eat.
occurred to me that there was no time to loss.
is good to be sitting in the sun.
mother warned the children time and again not to play with fire, but the children didn’t take it seriously.
won’t take long to get to Haikou by plane.
’s great fun riding a horse.
17. (The storm stopped.) Now it has cleared up.
was part of the province that was flooded.
arrived late.
’s a fine day, isn’t it!
A：7, 10, 11, 14, 19 B：2, 3, 6, 9, 15, 17, 20
C：4, 5, 12, 13, 16 D：1, 8, 18
II 单项填空
1.______ is ______ who wants to see you.
…he …he …him
2.______ used to be thought that the earth was square.
3.I found ______ impossible for _____ to work out the maths problem.
…he …he …him …him
4. -Do you have my pen, Mary?
-Yes，I have ______ right here.
arrived half an hour late,_____ made us unhappy.
h
learned Chinese for about two years，______ is, from 1993 to
1995．
______ matter if he can’t finish the job on time?
8.-Hello, who is _______ speaking?
-_______ is Tom speaking．
…It …That …This …He
9.______ ought to be no trouble because he knew the answers．
e
10.-Is it going to snow tonight?
-I' m afraid ______ ．
think ______ possible to learn a foreign language while
studying in the middle school.
are is
12. -Who is knocking at the door?
- .
A.I’m, Mary ’s me, Mary ’s me ’s me, Mary
thought a great honour to be invited to speak to us.
is
______ necessary to complete the design before National Day?
15. She heard a terrible noise, _____ brought her heart into her mouth.
h C. this