语法精讲 IT的用法
1.用作人称代词，代替前文提到过的事物
The frog is not a warmblooded animal.It is cold-blooded one.
2.用以代替指示代词this,that
—What is this?
—It is a flag.
—It is hers.
3.起指示代词的作用，指一个人或事物
—Who is knocking at the door?
—It is me.
—Who is making such a noise?
—It must be the children4.指环境情况等
It was very quiet(noisy)at the moment.
5.指时间、季节等
—What time is it?
—It is eight o’clock.It often rains in summer.
6.指距离
It is five kilometers from the office to my home.
7.形式主语it的用法
It is+clear+that
(2)It is+cruel(kind,brave,nice,rude,wise,stupid,clever,foolish,polite…)+of sb.+ to do sth.
(3)It is important(necessary,possible,impossible,easy,difficult,hard…)+for sb.+to do sth.
①It is foolish of you to waste money.
②It is silly of him to say that.
介词for和of的区别依前面的那个形容词而定。如果那个形容词指的是一种行为的性质，就要用for;如果那个形容词指的是行为的性质，同时又指行为的人，就用of。换句话说，单说行为的用for,如necessary一词，仅指“行为”，而无法指“行为者”；而说及行为者的用of，如kind一词，可以说“你的行为是亲切的”，也可以认为作为“行为者的你是亲切的”。
①It is rude for the young to make fun of their elders.
②It was very kind of your uncle to give us a lift in his car.
①It seems that he is ill.
②It happened that he wasn’t at home.
8.形式宾语it的用法
I+believe(make,consider,regard,suppose,feel,think,find,…)+it+宾语补足语+to do如：I think it important to work hard every day。
9.用于强调结构
要强调句子的某一部分（通常是主语、状语、宾语），可以把it当作先行词。这种句子的结构是“It is(was)+被强调部分+that(who,whom)+句子的其余部分。”如果强调的部分是人，可用who,whom代替that。例如：
It is Prof.Lin who teaches us English.(强调主语)
It is English that Prof.Lin teaches us.(强调宾语)
It was in Shanghai that I saw the film.(强调状语)
It was in 1975 that I worked in a factory.(强调状语)
【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: if I can help it意为“如果我有办法”，表示有办法做某事，或有办法控制某个局面。所提供的情景“I don’t like working late into the night”说明如果有办法，不喜欢工作到深夜。so意为“这样”，常用于省略句中，代替上文中的动作。that用于代替上文的内容。
答案：C
【考例2】2006山东高考，24I’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指代用来泛泛地指某事，可用于如I like it, I appreciate it等类似的句子，表示喜欢和赞赏某事，it和that均可指代前面提到的名词或事，it是人称代词，可指代同名同物，指代有不定冠词的或有其他限定词的单数可数名词，也可指代一件具体的事；that是指示代词，常指代有定冠词的单数可数名词和不可数名词，也可指代刚提到的一件具体事。
答案:B
【考例3】2006安徽高考，34Catherine bought a postcard of the place she was visiting,addressed________to______and then posted it at the nearby post office.
A.it;her
B.it;herself
C.herself;her
D.herself;herself
解析:address sth. to sb.“把（话）讲给……，把（信）写给……”。
答案：B
【考例4】2006江苏扬州一模in the school rules that boy students should not wear long hair.
A.What is required
B.What requires
C.It is required
D.It requires
解析:考查名词性从句。it是形式主语，that引导的从句是真正的主语。
答案：C
【考例5】2005山西太原一模We have made______a rule to practise oral English whenever and wherever_______possible.
A.it;its
B.it;it
C.that;it
D.it;/
解析:考查代词it的基本用法。it可作形式主语和形式宾语，无意义，真正的主语和宾语后置。make it a rule to do…即为该用法，第二空为省略句，在时间和条件状语从句中，从句的主语是it,谓语是be动词，此时it is/was可一同省略。
答案： D
【考例6】2006黄冈一模—He looks unhappy.
—Yes,but he can’t say what it is_______is bothering him.
A.as
B.that
C.what
D.which
解析:考查强调句型。...“what it is that is bothering him”是强调句型。
答案：B