it的用法及强调句型it的用法一、it作指示代词【完成句子】用one，ones，it，that，those填空(1) — I can't find my watch.—You haven't found ______？If you want to buy a new ______，I suggest you buy ______ made in China.(2) We've got a big cup and two small ______.(3) The weight of an elephant is much greater than ______ of a tiger.(4) The books on the first shelf are easier than ______ on the second shelf.(5) The boy told his story and ______ of the girl upstairs.【答案】(1) it; one; one (2) ones(3) that (4) those / the ones (5) that / the one【结论1】①指代上文提过的事物时，it指的是同名同物，相当于the＋名词；②one指的是同名异物，表示单数可数名词相当于a ＋名词；a / an＋形容词＋one等于a/ an＋形容词＋名词；复数形式用ones；③that后面常有后置定语，有特指意义，代替不可数名词或单数可数名词，相当于the＋名词；④复数名词用those，相当于the ones。
【例句观察】— Someone is knocking at the door. Who is it?— It must be Leo. He said he'd come to see me.【结论2】it指代人时，常指小孩或身份不明的人。
【例句观察】It's too quiet in the room. Everyone just keeps silent.【结论2】it可用以指代环境或情况。
(6)— What time is it now? — It's half past seven.(7)— It is spring now and it's warm these days.【结论3】it可用以指代时间、季节、天气或距离。
【注意】it指代时间时，有如下一些句型：(1) It is time for sth. (for sb.)to do sth. / that－从句(should do / did, 必须用虚拟语气)例：① It's time for lunch.② It's time for us to clean the house.③ It's time that we should clean the house. ＝It's time that we cleaned the house.(2) It is / has been ＋some time ＋since－从句(从句用一般过去时)It is 10 years since I graduated from college.(3) It / This/That is the first / second time that－从句(必须使用现在完成时)这是某人第……次做了某事。
It / This/That was the first / second time that－从句(必须使用过去完成时)例：①It is the second time that she has visited the Great Wall.②This was the first time that I had come late to school.(4) It was ＋时间点＋when －从句例：It was evening when we got home.＝It was evening in which we got home.(5) It was / will be ＋some time ＋before －从句例：①过了5年他们才从北大毕业。
It was five years before they finally graduated from Beijing University.②不久，我们就要从我们学校毕业了。
It won't be long before we graduate from our school.二、it作形式主语1.代替主语从句①It is clear ( obvious，true，possible certain....) that ..... “清楚（显然，真的，肯定．．．）”②. It is important ( necessary，right，strange，natural...) that ...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。
It is important that we (should) learn English well.③It is said (reported，learned....) that ...据说（据报道，据悉．．．）“。
It is said that he has come to Beijing.④. It is suggested ( ordered / demanded/ insisted/ commanded... ) that ...主句中的过去分词是表示请求，建议，命令等词时，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．．．）It is suggested that the meeting ( should ) be put off.⑤It is a pity ( a shame ... ) that ...that后的从句一般用虚拟语气（should + 动词原形），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。
It is a pity that such a thing should happen in your class.It is a pity that he is ill.⑥It 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。
It happened ( so happened ) that he met his teacher in the street. 碰巧．．.It seems that he will be back in a few days. 看来．．．It doesn’t matter if/whether they are old.It occurs to/strikes sb.＋that-clause 某人突然想到……It suddenly occurred to/struck me that I hadn’t seen Peter all da y.我突然想到，我一整天都没看见彼得。
How did it come about that－从句意为“……怎么发生的？”How did it come about that he knew where we were?How did it come about that so many people were attacked?2.替代不定式①. It takes sb. ... to do sth. ＂做．．．要花费某人．．＂It took thousands of people many years to build the Great Wall.②. It is kind ( of sb. ) to do sth.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 ，stupid ，wise wrong等。
这个句型可以改写为：sb. is kind to do sth. It is kind of you to say so. = You are kind to say so.③. It is necessary ( for sb. ) to do sth.常见的形容词有：①important，necessary，natural ②easy ，safe ，common ，normal ，hard ，difficult ,dangerous ，等。
在①中的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 party④It is up to sb. to do sth.“应由某人负责”或“……是某人的职责”。
It’s up to you to decide whether to take the job or not. 接不接受这份工作由你自己定。
3.作形式主语替代ing形式/It is worthwhile ＋doing sth./to do sth.It is no good (use )/useless doing sth. /It’s no pleasure doing sth. /It’s a waste of time doing sth.It is worthwhile spending/to spend much time on it. 在这件事上花时间是值得的。
It is no good learning English without writing English.It's useless trying to argue with Shylock.【结论】代替由不定式、动名词或从句所表示的真正主语。
为平衡句子，通常把不定式作主语改为it 作形式主语。
三、it作形式宾语【例句观察】①They found it difficult that they would finish their work in two days② She feels it hard to get in touch with her old friend.③ Mobile phones make it possible for us to keep in touch anywhere.④ I have made it a rule to get up early.⑤We think it our duty to clean our classroom every day. .【结论1】it 作形式宾语常用结构有：代替由不定式、动名词或从句所表示的真正宾语。