1.It's time(for sb.)to do sth./It's time for sth.译为“是(某人)该干……的时间了”、“到……的时候了”。如：

It's time for supper /to have supper.

2.It takes(sb.)some time to do sth.译为“(某人)花……时间做某事”。如：

It took me a week to finish reading the book.

3.It is one's turn to do sth.表示“轮到某人做某事”。如：

It's your turn to be on duty tomorrow.

4.It is /has been +时间段+since +一般过去时。译为“自从……以来已过了……(时间)”。此结构可以与另一种句型进行同义句转换。如：

It has been two weeks since we met last.=Two weeks has passed since we met last.

5.It seems /seemed +that从句。译为“看起来好像……”，此结构可以转换成“seem +不定式”形式。如：

It seems that he is ill.=He seems to be ill.

6.It's+adj.+of/forsb.+不定式。对于这个句型究竟用of还是用for，上面许振铎老师的文章中已有论述。这里再强调一下：如果形容词是描述不定式行为者的性格、品质的，如：kind，good，nice，clever等用of;如果仅仅是描述事物的形容词，如：difficult，easy，hard， important，dangerous等则用for。如：

It was very kind of you to visit me when I was ill.

It's important for him to learn English well.

7.It's+表语 +to do sth.。如：

It's a good idea to go out for a walk.=To go out for a walk is a good idea.

8.It's+adj.+ that从句。如：

It's true that he may fall behind the other students.