【知识点拨】
1.人称代词it，是第三人称单数中性，代表前文已提到过的一件事物。如：
1）I love swimming. It keeps me fit. 我喜欢游泳，它能使我保持健康。
当说话者不清楚或无必要知道说话对象的性别时，也可用it来表示。 如：
2）It’s a lovely baby. Is it a boy or a girl? 宝宝真可爱，是男孩还是女孩？
2.指示代词it，常用以指人。如：
1）Go and see who it is. 去看看是谁。
2）--- Who is making such a noise? -是谁发出这样的吵闹声？
--- It must be the children. -一定是孩子们。
3.it无指代性，常用作没有具体意义的主语，出现于表示天气、气候、温度、时间、地点、距离等意义的句子中。如：
1）It is half past three now. 现在是三点半钟。
2）It is six miles to the nearest hospital from here. 这里离最近的医院也有六英里。
3）It was very cold; it snowed and grew dark. 天气很冷；天下着雪，渐渐地变黑了。4.先行词it.
it充当形式主语或形式宾语，本身无意义，只起一种先行引导的作用，先行词不重读。后面的真正主语或真正宾语通常是不定式结构、-ing分词结构或名词性从句。
（1）用作形式主语
1）It is difficult to translate this article. 翻译这篇文章很难。
2）It is no use going there so early. 这么早去那里没有用。
3）It is strange that he did not come at all. 真奇怪，他竟还没来。
在上述诸例中，后置的真正主语可以取代先行it的位置，而出现于句首。
To translate this article is difficult.
Going there so early is no use.
That he did not come at all is strange.
（2）用作形式宾语
1）I found it difficult to explain to him what happened.
2）He thought it no use going over the subject again.
3）They kept it quiet that he was dead. 他们对他的死保密。
4）We must make it clear to the public that something should be done to stop pollution.
5. it为引导词的强调句型
它的结构形式是：It+be的一定形式+中心成分+that-/who-从句。
使用该句型有以下几点请注意：
①强调句的谓语is或was永远用单数，其中is既可强调现在的情况，也可强调过去的情况，was只能强调过去的情况。
例如：It was/is yesterday that I met your father in the street．
②不管被强调部分是哪种状语，只能用that连接，不得使用where、when等连词。
例如：It was in the street that I met your father yesterday．
③被强调部分为人时，可用who(主格或宾格)和whom(宾格)代替that，用that也行。
例如：It was your father that/whom /who I met in the street yesterday．
It was I that/who met your father in the street yesterday．
④强调句中也要注意主谓一致、人称一致和否定转移的问题。
例如：It is they who are our friends．（be）
It was until ten o'clock that we got home last night．(添加not)
⑤注意不要混淆强调句和其他从句。It is was…that…为强调句标志.
比较：It was ten o'clock when we got home last night．我们昨晚到家时已十点了。
It was at ten o'clock that we got home last night．我们昨晚是在十点到家的。
【知识过关】it用法演练
Task1 单项选择(32分)
1.It took us over an hour ________ along the street.
A. walk B. to walk C. walking D. walked
2.I think it a great honour _______ to visit your country.
A. to invite B. inviting C. having invited D. to be invited
3.Many people now make_______ a rule to buy cards for their friends before Christmas.
A. themselves B. it C. that D. this
4. ________ is very clear to everyone that he's round and tall like a tree.
A. This B. What C. That D. It
5.In the United States, bus travel doesn't cost much as train travel,________ ?
A. don't they B. does it C. do they D. doesn't it
6.Someone is at the door, who is_______ ?
A. this B. that C. it D. he
7.-It is raining cats and dogs.
- ____________. .
A. So it is B. So is it C. Neither it is D. Neither is it
8.-My home is in that tall building over there.
- __________ ?
A. Can it see B. Can see it C. Can be seen it D. Can it be seen
9. _________ raining hard for 3 hours without stopping.
A. It is B. It was C. It has been D. It had been
10.-Has the boy got his bicycle now?
-Yes, the police gave_________. .
A. him to him B. it to it C. it to him D. him to it
11.-Boy, ____________.
-It is, looks like spring is coming soon.
-Yeh, It'll just be a few more weeks.
A. it's really a nice day today, isn't it?
B. what knid of weather are we going to have today?
C. do you think it is going to rain today?
D. what' it like outside today?
12.It is important ________ their offer.
A. reject B. rejects C. to reject D. rejecting
13.Has ________ been decided when we are to hold the sports-meeting?
A. that B. this C. it D. what
14.-Did Li Lei call me while I was out?
-Yes, it was ________ that called you.
A. him B. he C. who D. whom
15.Nothing is wrong with the radio _________ ?
A. isn't it B. is that C. is it D. isn't that
16.I don't know ________ makes her afraid of having her business discussed.
A. what it is about Mary that
B. that is it abut Mary what
C. what is it about Mary that
D. that is about Mary what
17.Which sentence is wrong?
A.I felt it impossible for him to take the exam.
B.I found it impossible that he might take the exam.
C.I thought that he might not take the exam.
D.In my opinion he might take the exam.
18.I don't think _____difficult for a Chinese student to master a foreign language within five years
A. that B. it C. too D. very
19.It's the second time you _______ late this week.
A. arrive B. arrived C. have arrived D. had arrived
20.It will not be_______ we meet again.
A. long before B. before long
C. soon after D. shortly after
Task2．用it开头改写句子(14分)
1. Her sisters offered to pay her fare.That was generous of them.
2.Her brother invited her to stay. That was very kind of him.
3.You found your wallet. That is lucky.
4.You couldn't find a less expensive hotel. That is a pity.
5.To walk in the garden is pleasant.
6.To pronounce a long word is often difficult.
7.To learn a foreign language is very important.
KEY:
Task1．
1.B 2.D 3.B 4.D 5.B 6.C 7.A 8.D 9.C 10.C
11.A 12.C 13.C 14.B 15.C 16.A 17.C 18.B 19.C 20.A
Task2．
1.It was generous of them (her sisters) to offer to pay her fare.
2.It was kind of her brother to invite her to stay.
3.It is lucky that you found your wallet.
4.It is a pity that you couldn't find a less expensive hotel.
5.It is pleasant to walk in the garden.
6.It is often difficult to pronounce a long word.
7.It is very important to learn a foreign language.