it作形式主语
1.it be +形容词/过去分词+主语从句：
Example : It is important that we should exercise every day.
It was said that our school team won this football game.
2.it be+名词词组(a/an fact/pity/shame/honor/question)+主语从句：
Example:It was a pity that you didn’t come yesterday.
It was a question whether we can arrive there on time.
3.it +不及物动词(happen、appear) +主语从句
Example : It happened that he was her brother.
It appears that they meet at the school library.
3.it be +形容词 +for sb./of sb. to do sth.
Example : It’s very kind of you to help him with his English.
It’s necessary for us to master a foreign language
(小贴士：为什么形容词之后会有用for和of的区别呢?这其实是因为前面形容词的缘故，如果形容词在说sb.“很...”，后面介词就要用of;如果形容词在说to do sth.“很...”，后面介词就要用for )
4.it be+名词词组 +to do sth.
Example :It’ s my pleasure to help you.
5.it be+名词/形容词名词词组 (good/no good/no use/useless/senseless/a waste of) +动名词
Example :It is no good getting close to him.
It is a waste of time talking about such a boring question.
6.it take sb. some time/money to do sth.
Example :It takes him some time to finish his homework.
