语法精讲The Use of “It” (1) as Subject“It”的用法(1)作主语
1.it用作人称代词，指前面提到过的人或物。
The frog is not a warmblooded animal.It is a coldblooded one.
青蛙不是温血动物，而是冷血动物。(指代the frog)
—Who is knocking at the door?
谁在敲门？
—It is me.
是我。(指代人)
—What is this?
那是什么？
—It is a flag.It is hers.
是一面旗，那是她的。(指代this或that)
2.it也可用作非人称代词，表示天气、日期、时间、温度、距离、环境情况等。
It was very noisy at the moment.
现在外面很吵。(指环境情况)
—What time is it?
几点了？
—It is eight o’clock.
8点了(指时间)
It is five kilometers from the office to my home.
从办公室到我家5千米。(指距离)
3.it常用作形式主语或形式宾语，而把真正的主语或宾语(不定式、动词ing形式或名词性从句)置于句尾，以满足句子的需要。
it作形式主语，常用于下列结构：
1)It is+cruel(kind,brave,nice,rude,wise,stupid,clever;foolish,polite...)of sb. to do sth.
2)It is important(necessary,possible,impossible,easy,difficult,hard...)for sb. to do sth.如：
It is foolish of you to waste money.(=You are foolish to waste money.)
你浪费钱是愚蠢的。
It is necessary for us to study hard.(=To study hard is necessary for us.)
对我们来讲努力学习是必要的。
在这两个结构中，使用介词for还是介词of由前面的形容词而定；若形容词修饰人，使用介词of;若形容词修饰事，则使用介词for。
3)It is no use(useless,no good)doing sth.
It is no use talking with him.
跟他谈话是没有用的。
此结构中真正的主语通常为动名词。
4)It is said(known,reported,thought,hoped,believed,announced...)that...
It is said that he comes from America.
据说他来自美国。
此结构中真正的主语是名词性从句，且能变为简单句，上句可变为：He is said to come from America.即：从句的主语用作主语，谓语动词仍是主句的谓语动词，但应存在人称和数的变化，从句的谓语动词用不定式表示。如：
It was known that he had gone abroad.
=He was known to have gone abroad.
众所周知他出国了。
【考例1】2006全国高考Ⅰ,26If I can help _________,I don’t like working late into the night.
A.so
B.that
C.it
D.them
解析:此处考查it的用法。it可用于某些动词或前置词的后面，词义含糊，构成习语。如：You’ll catch it!你可小心点儿!此处If I can help it意为“如果我有办法的话”。有时我们也可以说It can’t be helped.或There is no help for it.表示“实在没法儿”。
答案:C
【考例2】(2006浙江高考，4)_______ is our belief that improvements in health care will lead to a stronger,more prosperous economy.
A.As
B.That
C.This
D.It
解析:本句考查从句的用法。根据句子结构，that引导的从句为主语从句，作真正主语，因此前边应有形式主语，而形式主语只能用it,不能用this或that。
答案:D
【考例3】(2006山东高考，24)I’d appreciate _______ if you would like to teach me how to use the computer.
A.that
B.it
C.this
D.you
解析:it作appreciate的形式宾语，真正的宾语是if you would like to teach me how to use the computer。it常在hate,like,appreciate等动词后作形式宾语，指代it之后的内容，对此用法应熟练掌握。
答案:B
【考例4】(2006全国高考Ⅱ,11) It is no _______ arguing with Bill because he will never change his mind.
A.use
B.help
C.time
D.way
解析:It is no use+doing...表示“做某事没有用”。it作形式主语，doing sth.作真正的主语。
答案:A
【考例5】(2006山东高考，33)Police are now searching for a woman who is reported to _______ since the flood hit the area last Friday.
A.have been missing
B.have got lost
C.be missing
D.get lost
解析:由句意可知“失踪”这一动作仍在持续中，故须用进行时态，又由since提示该句时态须用完成时态。
答案:A