四、It 作形式主语的常见句型：
1. 替代作主语的动词不定式，其句型为
(1) It be adj. (for sb.) to do sth.
此处adj. 通常为描述事件的形容词：easy, difficult, hard, necessary, unnecessary, possible, impossible, likely, unlikely, right, wrong, important, unimportant, legal, illegal, well-mannered, ill-mannered, polite, impolite, clear, obvious, certain, suitable, proper, fit, useful, useless, dangerous…例It is illegal (for a teenager) to drive a car without a license.
(2) It be adj. of sb. to do sth.
此处adj. 通常为描述人的形容词：kind, unkind, nice, rude, cruel, considerate, thoughtful, thoughtless, careful, careless, silly, foolish, stupid, clever, wise, crazy.
例It's kind of you to help me with the problem.
(3) It替代作主语的动名词的常见句型
It's no good/use doing…It's (well)worth doing…It's (well)worth one's while doing/to do…It's (well)worth while doing/ to do例It's no use crying over spilt milk.
2. It替代作主语的从句常见句型
(1) It is + noun +从句例It is no secret that the president wants to have a second term at office.
(2) It is adj. +clauseIt's surprising that… (should)………竟然……It's a pity/shame that…(should)………竟然……例It's important that you should apologize to her for your rudeness.(=It's of much importance that you should apologize to her for your rudeness.)
(3) It verb sb. + clause= It is v-ing + clauseIt+surprise/delight/interest/disappoint/worry/disturb/annoy/amaze/bother/concern/frighten/please/anger sb. that…例It worried me that she drove so fast.(= It was worrying that she drove so fast.)
(4) It verb (to sb.) that…= sb/sth verb to do(verb = appear, seem, come about, emerge, follow, chance, happen, occur, transpire, turn out , work out)例It (so) happened/chanced that they were out.(= They happened/chanced to be out.)
(5) It is v-ed that…=sb/sth is to do(verb=say, report, think, believe, hope, expect, agree, accept, decide, determine, intend, plan, understand, know）例It is said that the couple have gotten divorced.(=The couple are said to have gotten divorced.)
(6) It is v-ed that … (should)…(verb=demand, request, require, order, suggest, advise, recommend例It is suggested that they should begin with the third question.
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