介绍:
It作形式主语常见句型
1.It + be +形容词+ that-从句
可用于此句型的形容词有: wonderful, true，good，right，wrong，（un）important，useless，surprising，disturbing,frightening,alarming,clear，unusual，lucky，certain, necessary等。 如： ① It is quite certain that he will be at the meeting.他将出席会议是无疑的。
② It is surprising that he came late to school this morning.他今天早上迟到真令人惊讶。 ③ It is important that we (should) study hard.我们努力学习是很重要的。
注意: 该句型中的形容词是（un）important, necessary等时，从句应为 (should )+动词原形。
It is important that we (should) learn English well.
It is necessary that he (should) remember these words.
2.It + be +名词+ that-从句
适用该句型的名词（词组）有: a pity，an honor，a good thing，a fact，a surprise，a question, a shame,a custom, a truth,our hope, no wonder, good/bad manners等。如：
① It is a pity (that) you missed the sports meeting last week. 你错过了上周的运动会太可惜了。
② It is a fact that English is being accepted as an international language. 事实上英语已经被作为一种国际语言而接受了。
3. It ＋seem／ appear／ happen的适当形式＋that从句。
① It seems that there is a big waste pipe coming down from the town.
②It appeared that he was calm, but inside his heart was beating wildly with fear.
4. It + be + 过去分词 + 主语从句，这类过去分词有：announced, believed, expected, hoped, decided, reported, said, shown等， 如：
It is reported that 16 people were killed in the earthquake.
It is not decided who will give the operation to the patient.
5. It is time ( about time ,high time ) that ...
该句型中that 后的从句应该用虚拟语气，值得注意的是① 常用过去时态表示虚拟．② 有时也用should + 动词原形，should 不能省。常译为＂是（正是）．．．的时侯．．．＂。 It is time that children should go to bed.
= It is time that children went to bed.
6. It is the first ( second ... ) time that ...
用完成时态。至于用什么完成时态，由主句的谓语动词的时态决定。如果是一般现在时，后面从句用现在完成时态；如果是一般过去时，后面从句则用过去完成时态。该结构中 that 可以省去；it有时用 this 替换．常译为＂是第一（二）．．．次．．．＂。
It is the first time I have been here.
= This is the first time I have been here.
7. It + be + adj./ n. (for sb. / of sb.) + to do sth. 该句型中的形容词通常是表示事物的特点或特征的如difficult，hard，easy，impossible，necessary，important等，此时用for；或表示人的性格特征或特点的如nice，good，bad，kind，silly，foolish，wise，clever， careless，rude，brave，cruel，careful， grateful等，这时要用 of。如：
① It is foolish of you to give up such a good chance.
② It is necessary for college students to master at least a foreign language.
