发布者：王樱樱 所属单位：平顶山市第三十一中学 发布时间：2018-05-16 浏览数( -) 【举报】
It 用作形式主语
当不定式（短语）、动名词（短语）或从句在某个句子中作主语时，为保持句子结构前后平衡，避免头重脚轻，因此常用it作形式主语置于句首，而将真正的主语放在句尾。此时it只起先行引导作用，本身无词义。
一、 代替动词不定式做主语
拒绝是令人遗憾的。
It’s a pity to refuse.
记住这点是很重要的。
It’s very important to remember this point.
1. It + be + 形容词 + for sb + to do sth
这类句型常用形容词(通常为描述事件的形容词)easy, difficult, hard, important, possible，wise, necessary, impossible, likely, obvious, useful, 等作表语，有时候为了强调不定式动作的执行者，常在不定式前加for sb，译为“对某人来说做某事怎么样”
It’s necessary for the young to master two foreign languages.
It is unwise to give the children whatever they want.
2. It + be + 形容词 + of sb. + to do sth
这类形容词常是表示心理品质,性格特征的形容词，如：kind, nice stupid, clever, foolish, polite, impolite, silly, selfish, considerate等。某人和这些形容词可以构成主系表结构。
It’s very kind of you to help me with the work.
=You are kind to help me with the work.
It’s foolish of you to drive a car after drinking.
=You are foolish to drive a car after drinking.
3. It + be +名词词组 + to do sth
It is not a good habit to stay up too late.
4. It takes/took sb +some time/ money to do sth做某事花了某人多长时间或多少钱
It took the workers almost three years to finish building the dam.
It will take a whole day to get to the top of the mountain on foot.
二、 it代替动名词做形式主语
It is no good use crying over spilt milk. (覆水难收)
It is no use casting pearls before swine. (不要明珠暗投，对牛弹琴)
It + be + 名词或形容词 + 动名词
这类名词和形容词常常是：good, no good, no use, a waste of…, useless, senseless等
It’s a waste of time talking to her any more。
It is no use arguing about the matter with him.
三、 it代替从句做主语
1. it + be + 名词词组 + 主语从句
这类名词有：a fact, a pity, a shame, an honor, a question, a surprise……..
It’s a pity that you lose your money
2. it + 不及物动词+ that(as if )+ 从句
这类不及物动词有：look, seem, appear, happen, occur,
It seems that he does not tell the truth.
It occurs to me that I forgot to lock the door!我突然想起我忘记锁门了
3. it + be + adj + that从句
It is necessary/impossible/important/natural that sb. (should) do sth.
It’s important that we (should) keep the balance of nature
4. it + be + -ed(过去分词)+ that 从句
it is said that …….. 据说……..
it is reported that ……… 据报道
it is supposed that…… 据推测
it is well known that …… 众所周知
it is generally considered that … 普遍认为
it is suggested that …… 有人建议