一、It是代詞
指除人以外的一切生物和事物，用來指代時間、季節、天氣距離、環境。在這裡，i是一個虛詞，沒有任何實際意義。例如:
①It is a quarter to eight now.
現在是八點差一刻。
②It is midnight. 現在是午夜。
③It is time for breakfast.
現在是吃早飯的時間。
④-What is the date today?今天幾月幾號?
--It is December 3rd. 十二月三號。
⑤--What season is it?現在是什麼季節?
--It is summer. 夏季。
⑥--What is the weather like today?
今天天氣如何?
--It is fine.天氣很好。
--It is foggy and wet.天氣多霧又潮溼。
⑧How far is it from the bus station to your home? 從汽車站到你們家有多遠?
⑨It is around five miles to the shopping center.從這兒到購物中心大約有五英里。
二、It用作主語
用來指代文中出現過的人或事。
it此時可用來代替一個名詞，一個短語，一個從句或一個句子。在句中可指生物,非生物，不明性別的人，也可以指一個動作或件事情(人物型)，還可以指人或事物的身份(指示型)。在這裡,it是有實際意義的。例如:
①--What is this?這是什麼?
--It is a computer.這是一臺計算機。
②--What is that?那是什麼?
--It is a map.那是一張地圖。
③--Where is the dog?狗在哪兒?
--It is lying under the tree.它在樹下面躺著呢。
④--Where is the post office?郵局在哪兒?
--It is near the hospital 在小醫院附近。
⑤--Who is that man?那個人是誰?
--It is my brother.是我哥哥。
⑥He tried to get rid of smoking，but it was impossible.他嘗試著戒菸，但那是不可能的。
⑦If you exercise every day ,it will keep you well and strong.如果你每天鍛鍊，你就會變得健康。
三、It作形式主語
為了避免將句中作真主語的不定式、動名詞和名詞子句置於句首造成頭重腳輕，習慣上it可作為形式主語置於句首，指代後面的真正主語，使句子顯得流暢。it 作形式主語的句型有:
It+謂語+不定式
It+謂語+動名詞
It+謂語+名詞性從句
1.不定式具有名詞的性質，在句子中可作主語。例如:
It is wise to understand each other
=To understand each other is wise.
互相理解是明智的
記：把it翻譯為中文時,it沒有實際意義，要把後置的不定式作為主語來翻譯。例如:
①It is necessary to have a good sleep before the test for us.
= To have a good sleep before the test for us is necessary.
對我們來說考試前好好睡一覺是很必要的。
②It is wrong to do so.=To do so is wrong.
這樣做是錯誤的。
③It is a bad habit to eat junk food.
= To eat junk food is a bad habit.
吃垃圾食品是一種壞習慣。
④It took us 12 years to complete the project.
= To complete the project took us 12 years.完成這項工程花費了我們十二年的時間。
2.與不定式不同,動詞-ing作主語時一般置於句子開端;置於句尾時則常將動詞-ing改成不定式。因此用it代替動詞-ing作形式主語的句子較少，主要用在以no use，useless, not any use, not much use, not any good, not much good, no good, no help, dangerous，senseless, worth ，while ,a waste 等詞作主語補足語的句子中。例如:
①It is no use arguing with the people who won't see reason.和不講理的人爭論是無用處的。
②Is it any good( any use ) making such a decision?做這樣一個結論有用嗎?
③It is dangerous playing with fire. 玩火是危險的。
④It is worth reading the book.
讀這本書值得一讀。
四、It可代替由that、連接代詞或連接副詞引導的名詞性從句。
①It was clear that he had desire for peace.
= That he had desire for peace was clear.
很清楚他有和解的願望。
②It was reported that the new president had been elected.
= Thatthe new president had been elected was reported.
據報道新總統已被選出來了。
③It is a pity that her sister cannot go shopping with us.
= That her sister cannot go skating with us is a pity.
她的姐姐不能和我們一起去購物,這太令人遺憾了。
五、It +名詞性從句的結構一般可歸為六類。
1.It+be動詞+形容詞+that從句
①It is strange/ obvious natural good/ possible/ funny/ surprising/usual +that從句。例如:
②It is strange that nobody knows where he lives.奇怪的是，誰也不知道他住在哪裡。
2.It +be動詞+名詞+that從句
It is a fact/ an honor/a good thing/ good news/a pity + that從句。例如:
It is a pity that you didn't come.
你沒來，好遺憾。
3. It was said/reported/ announced/ expected/ decided + that從句。例如:
①It's said that he has performed many miracles.據說他創造了許多奇蹟。
②It was reported that muscle diseases were increasing rapidly.
據報道肌肉疾病正迅速增加。
4.It seems/happened/ turned out/occurred to me + that !從句。例如:
It seems that my teacher knows a lot about this.我的老師對這件事知道的似乎很多。
5. It is doubtful/a question/ uncertain/a mystery+連接代詞或連接副詞引導的子句。例如:
It is a question whether she would play the part. 她是否能扮演這個角色還是個問題。
6. It doesn't matter/ doesn't make too much difference +連接代詞或連接副詞引導的子句。例如:
It doesn't matter whatever you do.
無論你做什麼都沒關係。
六、It的強調句型
句子結構：It+be動詞+被強調的成分+子句。It此時是沒有實意的虛詞，它的作用是強調放在主語補語位置的某個句子成分。當強調部分指人時，可用who( whom)/that,其他情況下多用that,不能用which。
1.強調主語
①It was his brother who/ that broke the cup.是他的哥哥打碎了杯子。
②It was two pupils who/ that helped the blind man cross the street.是兩個學生幫助這個盲人過馬路。
③It is the people who/ that are really powerful.人民是真正有力量的。
④It is Professor Smith who/ that teaches us chemistry every Monday afternoon.是史密斯教授每週一下午教我們化學。
2.強調賓語
(1 )強調直接賓語。例如:
①It is chemistry that Professor Smith teaches us every Monday af-ternoon.史密斯教授每星期一下午是給我們講化學。
②It was a New Year card that he sent his classmate.他寄給他同學的是張新年卡片。
(2)強調間接賓語。例如:
①It was his classmate whom/ that he sent a New Year card to.他將新年卡片寄給他的同學。
②It was the guard whom/that he showed the pass to.他將通行證出示給警衛。
③It is us whom/that Mr Li teaches chemistry every Monday afternoon.李老師每週下午給我們教化學。
8.強調狀語
(1)強調時間狀語。例如:
①It is every Monday afternoon that Mr Li teaches us Maths.李老師給我們講數學課是在每星期一下午 。
②It was not until Saturday that he began to prepare the examination.他直到星期六才開始準備考試。
(2)強調地點狀語。例如:
①It might have been on the bus that I lost my purse.
我可能在公共汽車上丟失了皮夾。
②It was before the fireplace that the old woman was sitting.
這位老婦人坐在壁爐前。
4.強調賓語補足語
①It was white that my aunt painted her bedroom.
我的姑姑把臥室漆成白色。
②It was captain that the team chose him.
隊員們選他當隊長。
③It was wrong that we considered him.
我們認為他是錯誤的。
④It is a fine player that we believe Jane.
我們相信珍妮是一個出色的選手。
5.強調主語補足語
It is Little Tiger that he is called.
他被稱作小老虎。
七、It用在一些習語中作 主語
It cannot be helped.沒有辦法。
It is hard to say.很難說。
It comes to nothing.沒有什麼結果.
八、It作真正賓語
①She is very stubborn though she does not look like it.
她非常固執，雖然看上去並非如此。
②When he found what the world needed, Edison went ahead and tried to invent it.
當他發現世上需要的東西時，愛迪生總是盡力去發明它。
③You'd better have a try and you will find it quite interesting.你最好嘗試一下，就會發現這很有趣。
九、It作形式賓語
1.代替不定式。例如:
①Mike found it interesting to read the book A Tale of Two Cities.
麥克發現讀小說《雙城記》很有意思。
②She made it her business to take care of her younger sister after her mother died.
在她媽媽死後，她認為照顧妹妹是自己的責任。
2.代替動詞-ing。例如:
①He thinks it sheer waste of time arguing with a madman.他認為和一個瘋子爭論純粹是浪費時間。
②Don't you think it wrong wasting your time? 你不認為浪費時間是錯誤的嗎?
3.代替that引導名詞性從句。例如:
We should make it clear to the public that we are doing an im-portant job.
應向公眾表明我們正在進行一項重要的工作。
I considered it true that he was ill.
我認為他病了，這是真的。
十、試題與解析
選擇最佳答案填空。
1. Was it in 1969（）the American astronauts succeeded（）landing on the moon ?
A. when ;on
B. that;on ,a
C. when;in
D. that;in
2.（）in the park tomorrow.
A. It will lovely
B. It will be lovely
C. There will be
D. There will
3. In fact,（）is a hard job for the police to keep order in an important football match.
A. this B. that C. there D. it
4. How much does（ ）to rent a car?
A. it costs B. costs C. it D. it cost
5. What a mistake（ ） to come here!
A. it B.is,era C. is it D. it is
6.（ ）easy thing to master a skill.
A.It is not a
B.It not is a
C.It is not an
D. It not is an
7.（ ）that Miss Smith knows a lot about history.
A. It seemed
B. It seems
c. It is seemed
D. It was
8.（）too much difference who is in charge of the supermarket.
A. It doesn't make
B. It is make
c. It doesn't made
D. It is made
9. It（ ）in the morning , but now it has cleared up.
A. is cloudy
B. was cloudy
c. was cloud
D. is cloud
10. I hate（）when people talk with their mouths full.
A. it B. that C. these D. them
11. It（）when the new road will be opened to traffic.
A. is made clear
B. had be
c. made clear
D. was made clear
12.（）to Mr. Jackson how he became a writer.
A. It has mystery
B. It is mystery
c. It has a mystery
D. It is a mystery
13. People（）that the earth is center of the universe many
years ago.
A. took this for granted
B. took it for granted
c. took that for granted
D. took its for granted
14. It looks as if（ ）going to rain.
A. it were
B. there is
с. it is
D. there are
15.（）whether he will visit that country.
A. It is not decided
B. It decided not
с. It not decided
D. It was not decided
16. It ’s that he has retired.
A. is appeared
B. appearing
C. was appeared
D. appears
17. --Wasn't it Dr. Want who spoke to you just now?
--（ ）.
A. I didn't know he was
в. Yes, it was
с. No , he wasn't
D. Yes ,he did
18.（ ）a long time since he last visited his hometown.
A.It is
в. It was
с. They are
D. They have
19.（ ）to use our time wisely.
A. We are good
в. It is important for us
с. We are important
D. It is important to us
20.（ ）going shopping on Sundays.
A. It is pleasure
в. It is a pleasant
C.It is a great pleasure
D. It is a great pleasant.
答案：
1 ~ 5. DBDDD
6~ 10. CВABA
11 ~ 15. ADBCA
16 ~ 20. DBABC
