英语语法：高中英语It的用法
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一、It用作实词
表达以下概念:指代前文提到的事物，如前文中的this, that；替代前文中的内容；指代一位性别不明的小孩或未知的人；指代未指明但谈话双方都知道的那件事；指代时间、天气、气候、距离等自然现象……
二、It用作形式主语
替代作主语的从句、动词不定式、动名词，而把真正作主语的从句、动词不定式、动名词置于句尾。
It 作形式主语的常见句型：
1. 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, uful, uless, dangerous…
例: It is illegal (for a teenager) to drive a car without a licen.
(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, wi, 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/u 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 u crying over spilt milk（覆水难收）.
2. It替代作主语的从句常见句型 ：
(1) It is + noun +从句
例: It is no cret that the president wants to have a cond term at office.
(2) It is adj. +clau
It’s surprising that… (should)………竟然……
It’s a pity/shame that…(should)…老虎简笔画图片
……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. + clau= It is v-ing + clau
It+surpri/delight/interest/disappoint/worry/disturb/annoy/amaze /bother/concern/frighten/plea/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
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, advi, recommend
例 It is suggested that they should begin with the third question.
三、It作主语的句型
1. It takes sb. … to do…(=sb takes…to do…)某人用多长时间做某事
例: It took the men a week to mend our roof.(= The men took a week to mend our roof.)
2. It’s (just)(un)like sb. to do…（不）像某人做某事的风格
例: It was (just) like him to think of helping us.
3. It’s (about/high) time that… should /v-ed…是该做某事的时候了
