It用法小结
it在英语语法中属人称代词,意思是“它”,用来指人以外的一切生物和事物.它的用法不仅不简单,而且很复杂.
一、用于指人以外的一切生物、无生命的东西和事情.
一般指说话者心目中已经了解或所指的生物、无生命的东西或事情、没有性别的区分；可以是可数名词,也可以是不可数名词,在句子中既可作主语,也可以作宾语.
1．指动物和植物.如：
—Oh,that's Lucy's hat．噢,那是露茜的帽子.
—It looks like a cat!它看上去像只猫!
Where's tea grown?It's grown in the southeast of China．
什么地方种植茶?中国东南部种植茶.
2．指代一些无生命的东西.如：
Is it your watch?这是你的手表吗?
Look at the rain!It's heavy,isn't it?看这雨!雨很大,对吗?
3．代替上文提到过的整个事情.如：
Well,you mustn't play on the road．It's dangerous．哦,你不能在公路上玩.这太危险了!
It was hard work,but they really enjoyed it．摘苹果是艰苦活,可他们都乐意去干（它）.
二、用于指代人.
1．指代说话者心目中不太清楚的那个人,常在打电话或敲门时用.如：
—Who was it?是谁（打来的电话）?
—Was it Susan?（打电话的）是苏珊吗?
—Yes,it was．是的,我是.（根据上下句,“it was”也可不译出来.）
再如：—Who is knocking at the door?谁在敲门?
—It's me．是我.
2．指说话者心目中的那个人.如：
—Is it your sister,Kate?（那旧照片上的 baby）是你姐姐凯特吧?
—No!不是.
—Is it your brother?是你哥哥吧?
—No!不是.
—I know—it's you!我知道了,（那）是你.
3．指代性别不详的婴幼儿或在不计较性别时,也可用it来指人.如
The child smiled when it saw its mother．这小孩一见到母亲就笑了.
I don't know who it is．我不知道他是谁.
注意：看到这样的句子（或听到这样的话）时,要想一想,不要一看到it就把它译成“它”.）
4．在回答用指示代词表示人的特殊问句时,常用it指人.如：
—Who's that?那人是谁?
—Is it Kate?是凯特吗?
—Yes,I think you're right．It's Kate．是的,我想你说对了,是凯特.
三、用于指时间、距离和自然现象等.
1．表示时间.如：
—What time is it?几点钟?
—It's ten．十点钟.
It's summer in Australia now．现在澳大利亚是夏天.
特别注意it用于表示时间时还常见于以下两个句型中：
（1）It's time（for sb．）to do sth．／It's time for sth．译为“是（某人）该干……的时间了”、“到……的时候了”.如：
It's time for supper／to have supper．是吃晚饭的时候了.
I think it's time for us to start the lesson now．我想现在是我们开始上课的时候了.
（2）It is ／has been ＋时间段＋since ＋一般过去时.译为“自从……以来已过了……（时间）”.此结构可以与另一种句型进行同义句转换.如：
It has been two weeks since we met last．＝ Two weeks has passed since we met last．自从我们上次相遇以来,两个星期过去了.
It's three years since he came here．＝It has been three years since he came here．＝He has been here for three years．他到这里已经三年了.
2．表示距离.如：
It's half an hour's walk from my home to the school．从我家到学校步行得花半小时时间.
—Where's the farm,Li Lei?Is it far?李雷,农场在哪里?远吗?
—No,it's quite near．不,（距）离这很近.
3．表示自然现象.如：
Sometimes it snows and the land is all white．有时下雪,大地一片白.
It is very quiet here at the moment．眼下这儿很安静.
四、用作形式主语.
英语中常常见到某个句子以it开头,it与其后面的动词不定式短语、动名词短语、名词性从
句等相呼应,以表达一个完整的意义.这是一种习惯表达法,这样的句式可避免句子显得头重脚轻.
1．It＋is／was＋形容词＋（for／of sb．）＋动词不定式短语.对于这个句型中究竟用 for还是用of,一般遵循这样的规则：如果形容词仅仅是描述事物的形容词,如：difficult, easy,hard,important,dangerous等用for；如果形容词是描述不定式行为者的性格、品质的,如：kind,good,nice,clever等则用of.如：
It is interesting to play with snow in winter．冬季里玩雪是很有趣的.
It's important for us to keep the water clean．保持水质清洁对我们来说是很重要的.
It's very kind of you to say so．你这样说真是太好了.
注意：这一句式中的形容词位置也可换用名词；连系动词be也可换用其它连系动词,如feel等.如：
It's a good habit to get up early and go to bed early．早睡早起是好习惯.
It must be great fun to fly to the moon in a spaceship．乘宇宙飞船飞往月球一定很有趣.
It feels strange to have a twin sister．有个孪生姐妹感觉很奇怪.
2．It ＋will be／is ／was ＋形容词＋动名词短语.如：
It's bad playing in the street．在街上玩是没好处的.
Is it any good trying again?再试一次有用吗?
3．It＋is／was＋形容词＋从句.如：
It is certain that he will come．他一定会来.
It's true that he may fall behind the other students．他真的可能落后于其他同学.
It is strange that he should say so．他居然这么说,真是奇怪.
4．It ＋is ／was ＋one's turn（duty,pleasure） ＋to do sth．意为“该轮到某人做某事（做某事是某人的责任、愉悦的事）”.如：
It's your turn to be on duty tomorrow．明天轮到你值日了.
5．It takes（sb．）some time to do sth．意为“（某人）花……时间做某事”.如
It took me a week to finish reading the book．我花了一周时间看完这本书.
6．It ＋cost／costs ＋sb．＋some money ＋to do sth．译为“某人花多少钱做某事”.如：
It cost me 260 yuan to buy the new watch．我买这块新手表花了260元.
7．It seems ／seemed ＋从句.译为“看起来好像……”,此结构可以转换成“seem ＋动词不定式”形式.如：
It seems that he is ill．＝He seems to be ill．看起来他好像病了.
五、用作形式宾语.
当句子的真正宾语是动词不定式、动名词或从句时,为避免句子头重脚轻,须将其放在宾语补足语之后,改用先行词it占据其原来的位置.it用作形式宾语的句型为：主语＋谓语＋it＋宾语补足语＋动词不定式／动名词／从句.该句型中宾语补足语可由形容词、名词等充当.如：
He found it not easy to learn a foreign language well．他发现学好一门外语是不容易的.
We think it no good reading in bed．我们认为躺在床上看书无益处.
I think it necessary that we have the meeting．我认为开这个会是必要的.
