在英语学习中，我们不要小瞧一些看似简单的单词，比如 it。它虽然在拼写上极其简单，但是其用法却有很多种。不信的话我们就一起来看看吧！
1. It is+被强调的部分+ that...
该句型是强调句型，将被强调的部分放在前面，其他部分置于之后，强调的部分如果是人，则可用 who/ whom来替换（但如果被强调的部分既包括人又包括物的话，只能用 that）。如果把这种句型结构划掉后，应该是一个完整无缺的句子，这也是判断强调句型与其他从句的方法。
It was they who cleaned the classroom yesterday.
It was in the street that I met her father.
It is the famous writer and his works that have aroused great interest among the students.
2. It is not until+被强调的部分+ that...
该句型译成汉语“直到……才”，可以说是强调形式。
It was not until she took off her dark glasses that I realized she was a film star.
= Not until she took off her dark glasses did I realize she was a film star.
= I didn't realize she was a famous film star until she took off her dark glasses.
3. It is clear( obvious, true, possible, certain...) that...
该句型中 it是形式主语，真正的主语是 that引导的主语从句，常译为“清楚（显然、真的、肯定）”是主语从句最常见的结构。
It is very clear that he's round and tall like a tree.
= That he's round and tall like a tree is very clear.
4. It is important( necessary, right, strange, natural...) that...
该句型和上一句同属一个句型。由于主句中的形容词不同， that后的从句中要用虚拟语气（ should+动词原形），其中 should可以省去，建议记住该句型中的形容词。
It is important that we (should) learn English well.
It is necessary that he (should) remember these words.
5. It is said( reported, learned...) that...
该句型中的 it仍是形式主语，真正的主语是 that引导的主语从句。该结构常译为“据说；据报道；据悉……”。
It is said that he has come to Beijing.
It is reported that another earth satellite has been put into orbit.
6. It is suggested( ordered...) that...
该句型和上一句属一个句型。主句中的过去分词是表示请求、建议、命令等词时， that后的从句要用虚拟语气（ should+动词原形），其中 should可以省去，常译为“据建议；有命令……”。
It is suggested that the meeting (should) be put off.
It was ordered that we (should) arrive there in two hours.
7. It is a pity( a shame...) that...
在该句型中， that后的从句一般用虚拟语气（ should+动词原形）， should可以省去，表示出乎意料，常译为“竟然”。没有这种意义时，则不用虚拟语气。
It is a pity that such a thing (should) happen in your class.
这种事竟然发生在你们班上，真是遗憾。
It is a pity that he is ill.
他生病了，真遗憾！
8. 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：常用过去时态表示虚拟，有时也用 should+动词原形，但是 should不能省。常译为“是（正是）……的时候”。
It is time that children should go to bed.
= It is time that children went to bed.
9. It is the first( second...) time that...
该句型应和上一个句型区别开来。该句型中不用虚拟语气，而用完成时态。至于用哪种完成时态，由主句的谓语动词的时态来决定。如果是一般现在时，从句用现在完成时态；如果是一般过去时，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……”。
10. It is... since...
该句型主要用作处理瞬间动词的完成时，要和表示一段时间的时间状语连用。主句中是时间作表语，其时态是现在时和完成时，引导的从句通常是一般过去时态，而且是瞬间动词。如果主句是一般过去时，从句则用过去完成时。
It is( has been) 5 years since his father died.
