1、 规则： (1)it指代上文提到的单数事物名词。 Could you find a dog in the picture? Yes，its in the park. (2)指代天气，时间，距离，温度和潮水等自然现象。 It was raining this morning. How far is it to the school? Its five minutes walk. (3)指代不知道性别的人。 Who is it? Its me.2it作形式主语或形式宾语的常见句型 (1)It is clear (obvious，true，possible，certain.)that. 该句型中it
2、 是形式主语，真正的主语是that引导的主语从句， 常译为“是清楚的(显然的，真的，可能的，肯定 的，)”，是主语从句最常见的句型结构。 It is very clear that hes round and tall like a tree.That hes round and tall like a tree is very clear.很清楚他像颗树一样又 圆又高。(2)It is important(necessary/right/strange/natural.)that.该句型和上面是同一个句型，由于本句型中的形容词不同，所以that后的从句要用虚拟语气(should动词原形)，s
3、hould 可以省略。It is necessary that we (should) remember these words.我们记住这些词汇很有必要(3)It is said (reported/learned.) that.该句型中it 仍是形式主语，真正主语是that 引导的主语从句。该结构常译为“据说(据报道，据悉)”It is reported that another earth satellite has been put into orbit.据报道又有一颗地球卫星送上了轨道。(4)It is suggested(ordered.) that.在本句型中，主句中的过去分词表
4、示请求，建议，命令等时，that 后的从句要用虚拟语气(should动词原形)，should 可以省略，常译为“有人建议(有命令)”It is suggested that the meeting(should) be put off.有人建议推迟会议。(5)It is a pity(a shame.)that.该句型中，that 后的从句一般用虚拟语气(should动词原形)，should 可以省略，表示出乎意料的结果，常译为“竟然”。没有这种意义时，则不用虚拟语气。It is a pity that such a thing(should) happen in your class.这种事
5、竟然发生在你们班，真是遗憾。It is a pity that he is ill.他生病了，真是遗憾。(6)It is time(about time/high time) that.该句型中that 后的从句应该用虚拟语气，值得注意的是；常用过去时态，有时也用“should动词原形”，should 不能省略，常译为“是(正是)的时候”。It is time that children should go to bed.It is time that children went to bed.到了孩子睡觉的时候了。(7)It is the first(second.)time that.该句
6、型要和上一个句型区别开来，该句型中的that从句不用虚拟语气，而要用完成时态，如果主句的谓语动词是一般现在时，后面从句用现在完成时态，如果是一般过去时，后面从句则用过去完成时，该结构中that 可以省略，it 有时用this 替换。常译为(是第一、二次)It is the first time I have been here.This is the first time I have been here.这是我第一次来这里。(8)It is.since.该句型主要用来处理瞬间动词和与表示一段时间的时间状语连用的问题，主句中是时间作表语，其时态是现在时或完成时，since 引导的从句通常是一般
7、过去时，而且是瞬间的动作，如果主句是一般过去时，从句则用过去完成时，It is(has been) 5 years since his father died. 他父亲死了5年了。(9)It is.when.该句型中的when引导的是一个时间状语从句，主句中的it 指的是时间，表语由具体的时间充当。常译为“当时候，是”。It was 5 oclock when he came here.当他来这里的时候是5点。(10)It be.before.该句型中的it 指时间，主句中的时态是一般将来时或过去时两种时态。主句中的表语多是long，not long,3 days,2 weeks等表示时间段的
8、词或短语。常译为“之前有多长时间”。It was 3 days before he went to Beijing.3天后他去了北京。It will be not long before he finishes his job.不久他就会做完工作。(11)It happens (seems/looks/appears) that.该句型中it 是形式主语，that引导的是主语从句，主句中的happen，seem 等词是不及物动词。意思是“碰巧”或“看来”等。It happened (so happened) that he met his teacher in the street. 碰巧他在
9、街道上遇到了他的老师。It seems that he will be back in a few days. 好像他过几天就回来。(12)It takes sb.to do sth.该句型中的不定式是真正的主语，it 是形式主语，句型中的直接宾语是时间，常译为“做要花费某人”It took thousands of people many years to build the Great Wall.修建长城花了成千上万人好多年时间。(13)It is no good(use) doing sth. 该句中的真正主语是动名词短语，主句中的表语可以是no good(not any good)，n
10、o use(not any use)。It is no good learning English without speaking it.学英语不说英语是没有用处的。(14)It is kind(of sb.) to do sth.该句型中的不定式短语是真正的主语，如果不定式的逻辑主语由of引起，主句中的形容词必须是能表示逻辑主语特征的形容词。常见的有：bad，brave，careless，clever，cruel，foolish，good，honest，horrible，kind，lazy，modest，naughty，nice，polite，rude，silly，stupid，wise，
11、wrong等。这个句型可以改为sb.is kind to do sth.It is kind of you to say so.You are kind to say so.你这样说真是太好了。(15)It is necessary (for sb.) to do sth.该句型与上一个同属一个句型。如果不定式的逻辑主语由for引起，主句中的形容词通常是表示重要性，紧迫性，频繁程度，难易，安全等情况的形容词。常见的形容词有：important，necessary，natural，easy，safe，common，normal，hard，difficult，dangerous，unusual，r
12、are，impossible，pleasant等。前三个形容词作表语可以用从句改写，如：It is important for her to come to the party.It is important that she (should) come to the party.她来参加晚会很重要。(16)It looks(seems) as if.该句型中it无意义。as if 引导一个状语从句，常译为“看起来好像”，如果与事实不相符合，则用虚拟语气。It looks as if he is ill.(真的病了)It looks as if he were ill.(没有生病)(17)We
13、 think it important to learn a foreign language.该句中的it作形式宾语，为了方便记忆可称该句型为“6123”结构。6指主句中常用的动词：think，believe，make，find，consider，feel,1指的是形式宾语it,2指的是宾补的两种形式，形容词或名词。3指的是真正的宾语三种形式，不定式短语，动名词短语或that引导的宾语从句。We think it our duty to clean our classroom every day.我们认为每天打扫教室是我们的责任。He felt it important learning E
14、nglish well.他感到学好英语很重要。They found it difficult that they would finish their work in two days.他们发现两天内完成他们的工作很困难。3走出误区 (1)在“It isadj./n./过去分词that.”结构中that从句用虚 拟语气的情况要特别注意。常用的形容词有：strange， natural，proper，necessary，right，wrong，fortunate， important等。常用的名词有a pity，a shame，a desire等。 that从句中用“should动词原形”，sh
15、ould可以省略。(2)it 作指代用法时与one，that，those的区别it 替代上文提到的同一事物，该事物为可数名词单数或不可数名词。 Look! Its so good a ring，but I have no money to buy it.看，这戒指多好看啊，但我没钱买它。Do you have a camera？你有照相机吗？No，but my father has one.He bought it a week ago.没有，可我父亲有一架，他一个星期前买的。(3)one 替代上文提到的同类可数名词，表泛指，它的复数形式是ones。This is a point of idi
16、om rather than one of grammar. 这是习语的要点，而不是语法的要点。I want big apples，not small ones.我要大苹果，不要小的。(4)that可替代上文提到的可数名词单数和不可数名词，一般表同类中的特指。The weather in the north is better than that in the south.北方的天气比南方的好。The study of idiom is as important as that of grammar.学习习语和学习语法同样重要。(5)those 可替代上文提到的复数名词，前面可不用限定词， 但常有后置修饰语。The relics found were those of an earlier time.所发现的遗迹是较早年代的。
