I 人稱it
人稱it可以用來代替一個名詞、一個短語、一個分句或一個句子，避免它們在句中重復。
1.人稱it可以指事物、動植物或性別不明的嬰兒。
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.人稱it可以指包括許多成員在內的集體。
The Women’s Volleyball Team came back yesterday. It has just won the world championship.
3.人稱it可以指一個動作或一件事情。
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 +表語”結構中，指明某人或某物的身份的，具有這種作用的it可以用來代替this或that。(有語法學家稱其為指示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 無人稱it
無人稱it是虛詞，沒有任何具體的意義。
1. 無人稱it作主語，用于表示自然現象、時間、距離、環境狀況等句子中。
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. 無人稱it用在以seem, appear, happen, turn out 作謂語，后面跟that從句的句子中作主語。
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. 但不可以說 That he is always correct seems.)
3. 無人稱it作主語用于一些被動結構中。
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. 無人稱it作主語用于一些習慣用語中。
It makes no difference at all. 一點關系也沒有。
It’s hard to say. 這很難說。
It comes to nothing. 沒有什么結果。
It’s splendid ! 好極了！
III 先行it
先行it也是一個虛詞，在句中作形式主語或賓語。
1. 作主語
1) 真正主語是不定式短語。
It is impossible for me to get there the day after tomorrow.
It’s up to you to decide.
2) 真正主語是動名詞。
It’s no use trying to persuade him.
It’s no good your doing that over and over again.
3) 真正主語是名詞性從句。
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. 作賓語
用在“S + Vt + it + Co + O”句型中，這種句型中賓語較長而賓語補足語又較短，因此常用it作形式賓語而把真正的賓語放在賓語補足語的后面。
1）真正賓語是不定式短語。
I consider it better to be early.
2) 真正賓語是動名詞。
I don’t think it worthwhile taking so much trouble to do the job.
3) 真正賓語是名詞性從句。
I think it a pity that we shall never have such a chance again.
IV 強調it
強調it也沒有任何具體意義，強調it的句子結構是：
It + is/was + 被強調的成分 + that + 原句的剩余部分
被強調的成分通常是主語、賓語或狀語，強調由人所作的主語時，常用who替代that，所有的強調句均可以還原成陳述句。
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.
練 習
I 指出下列各句it的類型 (A-人稱 B-無人稱 C-先行 D-強調)
1.It is your daughter who has made that mistake.
2.It appears that he is intelligent.
3.It seems that we are mistaken.
4.It 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.
6.It is cold outside.
7.(What is it?) It is a ship near the horizon.
8.It was with great difficulty that the mountaineers reached the summit.
9.It was a warm summer morning.
10.(The train pulled in.) It was on time.
11.(I like fish.) It is goog to eat.
12.It occurred to me that there was no time to loss.
13.It is good to be sitting in the sun.
14.The mother warned the children time and again not to play with fire, but the children didn’t take it seriously.
15.It won’t take long to get to Haikou by plane.
16.It’s great fun riding a horse.
17. (The storm stopped.) Now it has cleared up.
18.It was part of the province that was flooded.
19.It arrived late.
20.It’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 單項填空
1.______ is ______ who wants to see you.
A.It…he B.That…he C.It..him D.That…him
2.______ used to be thought that the earth was square.
A.He B.What C.It D.That
3.I found ______ impossible for _____ to work out the maths problem.
A.it…he B.that…he C.that…him D.it…him
4. -Do you have my pen, Mary?
-Yes，I have ______ right here.
A.one B.it C.this D.that
5.He arrived half an hour late,_____ made us unhappy.
A.that B.it C.as D.which
6.Mary learned Chinese for about two years，______ is, from 1993 to
1995．
A.this B.that C.it D.he
7.Does ______ matter if he can’t finish the job on time?
A.this B.that C.he D.it
8.-Hello, who is _______ speaking?
-_______ is Tom speaking．
A.it…It B.that…That C.that…This D.it…He
9.______ ought to be no trouble because he knew the answers．
A.It B.There C.He D.That
10.-Is it going to snow tonight?
-I' m afraid ______ ．
A.it B.that C.so D.this
11.They think ______ possible to learn a foreign language while
studying in the middle school.
A.we are B.this is C.it D.that
12. -Who is knocking at the door?
- .
A.I’m, Mary B.She’s me, Mary C.He’s me D.It’s me, Mary
13.She thought a great honour to be invited to speak to us.
A.that B.this C.it D.it is
14.Is ______ necessary to complete the design before National Day?
A.he B.it C.that D.this
15. She heard a terrible noise, _____ brought her heart into her mouth.
A.it B.which C. this D.that