3.作形式主语替代动名词短语 It is no good / no use / useless doing sth. 常译为 “┅有好处或没有用” 　 　 ①It is no good learning English without speaking English. 　 ②It's useless trying to argue with Shylock.

= That　 he’s round and tall like a tree is very clear. ⑵It is important ( necessary， right， strange， natural...) that 从句 　常译为┅是重要的(必要的,对的,奇怪的,自然的┅).that 后的从句中要用虚拟语气(should + 动词原形)，should 可以省去，建议记住该句型中的形容词。 　 　①It is important that we (should) learn English well. 　 　 　②It is necessary that he (should) remember these words. 　⑶It is said (reported/ learned/believed/thought/known/told/hoped.....) that 从句 常译为＂据说(据报道，据悉．．．)＂。 　 　 　①It is said that he has come to Beijing. 　 　 　②It is reported that another earth satellite has been put into orbit. 　⑷It is suggested ( advised/ ordered / demanded/ insisted/ commanded... ) that 从句.that　后的从句要用虚拟语气(should + 动词原形)，should 可以省；常译为＂据建议；有命令．．．) 　 　 ①It is suggested that the meeting ( should ) be put off. 　 　 ②It was ordered that we ( should ) arrive there in two hours.

⑸It is time ( about time ，high time ) that从句(虚拟语气:动词用过去时did)

①　　 It is time that children went to bed.

②　　 It is time you bought a new car.

③　　 It is (high ) time you made up your mind.

⑹It is the first ( second ... ) time that从句(从句用现在完成时 have done )

　 It was the first ( second ... ) time that从句(从句用过去完成时had done )

　 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

⑺It is a pity ( a shame /an honour/a good thing/a fact,/a surprise/... ) that从句.　

that后的从句一般用虚拟语气(should + 动词原形)，should可省去．表示出乎意料，常译为＂竟然＂。没有这种意义时，则不用虚拟语气。 　 ①It is a pity that such a thing ( should ) happen in your class. 这种事竟然发生在你们班　　 上，真是遗憾！ 　 　 ②It is a pity that he is ill. 他生病了，真遗憾！

⑻It happens (seems， looks， appears ) that从句.常译为 “ 碰巧…,似乎是…,看起来…”

　　　 ①It happened ( so happened ) that he met his teacher in the street. 碰巧．．. ②It seems that he will be back in a few days. 看来．．．

2.作形式主语替代不定式　　 . ⑴ It is kind ( of sb. ) to do sth. 不定式的逻辑主语是由 of引起，主句中的形容词必须是能表示逻辑主语特征的褒义或贬义形容词。 常见的词有：

　bad ， brave ， careless， clever ， cruel ， foolish ， good (好心的)， honest ， horrible ， kind ， lazy ， modest ， naughty ， nice(有教养的)， polite， rude ， silly ， stupid ， wise ， wrong(错误的)等。

　这个句型可以改写为：sb. is kind to do sth. 。　 如:It is kind of you to say so. = You are kind to say so.

⑵It is necessary ( for sb. ) to do sth. .不定式的逻辑主语是由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，安全等情况的中性形容词。 常见的形容词有：

　important， necessary， natural easy ， safe ， common ， normal ， hard ， difficult ， dangerous ， unusual， rare ， impossible ， pleasant

如:It is important for her to come to the party. = It is important that she (should ) come to the party. ⑶It takes sb. ... to do sth. 常译为＂做．．．要花费某人．．．＂。 　 如:It took thousands of people many years to build the Great Wall.

①They watched the train until it disappeared in the distance. 2.，也可以指动物或婴儿(未知性别的婴儿或孩子):　

②Is this your dog？No, it isn’t.

③They got a baby and it was a ten-pounder 3.，也可指抽象事物或指抽象环境和情景:

③I hate it when people talk with a full mouth.． 二、.非人称代词 　1.it有时并不指具体的东西而泛指天气、时间、日期、距离、价值、度量、温度、环境等： 　 ⑴.指天气：It is a lovely day, isn’t　 it? 　 ⑵.指时间: It was nearly midnight when she came back.

⑶.指日期:It is April First today.

⑷.指距离:It is some 3000 kilometers from Beijing to Guangzhou.

⑸.指价值:It is three dollars.

⑹.指温度:Today it is 30 degrees centigrade.

3. What is more important， information superhighways can carry great amounts of information around the country quickly and cheaply.更重要的是，信息高速公路能把大量信息迅速、便宜地传遍全国。

2.　　　　　　 One day， it is said， Newton saw an apple fall from a tree.据说，有一天牛顿见到一个苹果从树上掉下来。

I am sure我可以肯定地说， I believe我相信， I wonder我不知道， you know你知道， you see你明白， that is也就是说， it seems看来是， as I see it照我看来， what is important (serious)重要(严重)的是， I?m afraid恐怕， it is said据说等。

1.　　　　　　 It will result in success， I suppose.我想，这件事终于会成功的。

2.　　　　　　 To start with， China is ready strengthen scientific and technological cooperation with many countries.首先，中国准备和许多国家加强科学技术合作。

strictly speaking严格地说， generally speaking一般地说， judging from…根据……判断等。

Judging from his letter， a campaign against“white pollution”has been undertaken in his hometown.根据他的来信做出判断，一场抵制“白色污染”的运动已经在他的故乡展开了。

注意:不要理解为现在分词短语作状语，因为上两句中speaking和judging的动作不是句中主语发出的。五、常用作插入语的不定式短语

to be sure无疑地， to sum up概括地说， to tell the truth老实说等。

1.　　　　　　 To be sure， community service can aid reemployment.

毫无疑问，社区服务能有助于再就业。

2.　　　　　　　 She knows much more about computer science than the other students do， for in stance.例如，她在计算机科学方面就比其他同学懂得多。

in a few words(或in sum， in short)简而言之， in other words换句话说， in a sense在某种意义上， in general一般说来， in my view在我看来， in his opinion(judgment)按照他的意见(判断)， in conclusion总之， in summary概括地说， in fact事实上， in the first place首先， in addition此外， of course当然， to our knowledge据我们所知， to my joy(delight， satisfaction)使我欣慰(高兴、满意)的， to their surprise(astonishment， amazement)使他们惊奇的， to her regret (disappointment)使她遗憾(失望)的， for instance(或example)例如， as a matter of fact事实上等。

1.　　　　　　 Of course， he did not succeed for the lack of experience.当然，他由于缺乏经验而未成功。