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, 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（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 secret that the president wants to have a second term at office.
(2) It is adj. +clause
It'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 + clause
It+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
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.
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
例: It's(about/high) time that we should take action.
4. It's the x-th time (that) … have v-ed…第几次做某事了
例: It's the third time that he has failed the driving test.
5. It is/has been… since …continuous v-ed(延续性动词) 某动作持续了多长时间
例: It's 10 years since he lived here
6. It was(not)… before…过(不)了多长时间某动作发生了
例: It was not long before they arrived.
四、It 作形式宾语
用来替代作宾语的从句、动词不定式、动名词，而把真正作宾语的从句、动词不定式、动名词置于句尾。
It 作形式宾语的常见句型：
1. verb+ it+ adj./noun (for/of) to do/clause (verb=think, believe, suppose, consider, feel, make, keep…)
例: I think it hard for you to do the task on your own./I think it hard that you'll do the task on your own.
2. verb+it+adj./noun (one's) doing (adj.=useless/worth/worthwhile)(noun=no use/no good/worth one's while/a waste of time/money/energy/words) (verb=think, believe,suppose, consider, feel, make, keep…)
例: I'll make it worth your while telling me about his secret.
3. verb+it+ important/unimportant/necessary/unnecessary/natural/essential that … (should)…
verb+it+of much/great/no/little importance that…(should)… (verb=think, believe, suppose, consider, feel, make, keep…)
例: I think it important that you (should) attend the conference.
4. verb + it+ as+ noun/adj.+ clause (verb=accept, regard, take, see, view)
例: The lecturer takes it as encouraging when so many students attend his lecture.
5. v. +it + prep. + that…
owe it to sb. that…把…归功于…
leave it to sb that…把…留给某人去做
take it for granted that …想当然
keep it in mind that…
例: Don't bother to arrange anything. Just leave it to me to sort out.
6. It用在不能直接跟宾语从句的动词后面，尤其是表示好恶的动词后，enjoy, like, love, dislike, resent, hate, don't mind, be fond of, feel like, see to 宾语从句紧跟it之后
例: I hate it you can swim so well and I can't.
7. It用在不能直接跟宾语从句的介词后面，宾语从句紧跟it之后（except that例外）
例: I'm for it that you will follow their advice.
让大脑放松的小窍门
伸个懒腰、闭眼眯一会儿、深呼吸几次……这些短暂的休息，能让高速运转的大脑得到充分休息。
抽10分钟就够了
如果学校没有午休时间，那就抽出10分钟午睡。这样做就能使人保持至少2小时以上精神活跃。如何用10分钟时间，打造一个完美的小憩?
选对时间。这10分钟最好在饭后，而且在11:00—13:00之间。 睡前设闹钟。许多人因担心睡过头，结果很难入睡，而设好闹钟会使人消除这一担忧。
听着“白噪音”。为了完美的午睡，应该找一个黑暗、安静的场所。如果必要的话，可以使用眼罩、耳塞，或者下载一些海浪声、风声等“白噪声”来排除干扰。
认真伸一个懒腰
伸懒腰能增加对心、肺的挤压，促进心脏泵血，增加全身的供氧，还有利于全身肌肉的收缩和呼吸加深。大脑血流充足了，人自然感到清醒、舒适。
伸懒腰时保持身体放松，将双手五指交叉，掌心向上置于头顶，脚尖交替伸直和上钩，四肢伸展的同时，还可以向左右转体，大约持续30秒钟。
发呆5分钟
专家研究显示，发呆是最简单的减压方式。
研究者发现，心无杂念、脑子里什么也不想的时候，大脑中的α脑电波得到加强。这种特殊的脑电波可以抑制信息超载，让注意力和意念更加集中，从而改善情绪，减轻压力，缓解焦虑不安，还能加强记忆力，缓解疼痛，并提高免疫力。
另有研究发现，每天适当发会呆能将焦虑和抑郁风险降低25%。 做个头部按摩
简单的头部按摩自己就能做，比如梳头疗法。选择个人比较能接受的力度，用十指指肚或指尖，从双眼眼眶上沿开始顺着往后梳头，梳至颈后风池穴，反复数次，也可以用牛角或实木梳子代替手指。
这个动作可以刺激头皮的神经末梢和经穴，有效松弛头部神经的紧张状态，促进局部血液循环，尤其是从事脑力劳动的人，每天坚持梳头3～5分钟，对于解除疲劳和大脑皮层的紧张状态大有好处。
吃点健康零食
在两餐之间或餐前吃点健康零食，既可以让你得到身心的放松，还有助于补充营养。
不妨在教室储备些零食，在上午10点或下午3点左右给自己来个短暂的“茶歇”，酸奶、水果、坚果等都是比较健康的零食选择。
出门晒晒太阳
晒太阳的好处不胜枚举，但国人晒太阳的时间仍远远不够。不妨在你感到疲倦时，把晒太阳这个功课补上。
上午10点和下午4点是晒太阳的最佳时间，此时可以散散步。可以多晒晒背部、双腿和头顶，有助于钙的吸收、合成，还能提高免疫力，每次晒15～20分钟为宜。
和别人分享一件趣事
欢笑是最好的减压良药。学习一两个小时后，和同学或家人分享一件趣事，或看看漫画书、搞笑视频等，都可以瞬间降低体内的压力激素。也可以走动一下，与同学聊聊天，身体也能得到放松。
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