一、以形式主语it引导的句型。
　　1. it (so) happened(chanced) that +clause. 碰巧…
　　= sb. happened /chanced to do sth. = sb. did sth. by chance.
　　it happened that he was out when i got there.当我到那儿时，碰巧他不在。
　　= he happened to be out when i got there./ it chanced that he was out when i got there./ he was out by chance when i got there.
　　2. it seems/appears that sb. do/ be doing/ have done/ had done 似乎…, 好像…
　　= sb. seems/appear to do/ be doing/ have done/to be done/to have been done
　　it seemed that he had been to beijing before. 他好象以前去过北京。
　　= he seemed to have been to beijing before.
　　3. it is / was+被强调的部分+that(who)+剩余的部分.
　　it wasn't until he came back that i went to bed. 直到他回来我才睡觉。
　　(一定要注意被强调句型中的谓语动词否定的转移)。
　　it was because he was ill that he didn't come to school today.
　　只因为他有病了今天没有来上学。(只能用because而不能用for, as 或since)
　　4. it is/was+表示地点时间/的名词+where/when +从句。
　　(注意本句不是强调句型，而是以where/when引导的定语从句。)
　　it was this house where i was born.请比较：
　　it was in this house that i was born.(后一句是强调句型。)
　　it was 1999 when he came back from the united states. 请比较：
　　it was in 1999 that he came back from the united states. (后一句是强调句型。)
　　5. it is / was said ( reported…)+that+从句. 据说/报道…
　　it was said that he had read this novel. 据说他读过这篇小说。
　　= he was said to have read this novel.
　　6. it is impossible / necessary/ strange…that clause.
　　(从句中的谓语用should+do / should have done，其形式是虚拟语气。)
　　it is strange that he should have failed in this exam. 真奇怪，他这次考试没及格。
　　7. it is + a pity/ a shame…that clause. (注意从句中的谓语动词用should do或
　　should have done的形式，但should可以省略。)
　　he didn't come back until the film ended. it was a pity that he should have missed this film.他直到电影结束才回来。他没有看到这部电影真可惜。
　　8. it is suggested / ordered/ commanded /…that +clause.
　　(从句的谓语动词用should do, 但should可以省略。)
　　it is suggested that the meeting should be put off. 有人建议推迟会议。
　　9. it is high time (time/ about time)+ (that) 主语+should do / did+其它。
　　是该做某