1. 人称代词it,是第三人称单数中性,代表前文已提到过的一件事物。如:
1)That vase is valuable. It's more than 200 years old. 那个花瓶很珍贵,它有200多年的历史。
2)I love swimming. It keeps me fit. 我喜欢游泳,它能使我保持健康。
当说话者不清楚或无必要知道说话对象的性别时,也可用it来表示。 如:
3)It's a lovely baby. Is it a boy or a girl? 宝宝真可爱,是男孩还是女孩?
4)The committee has met and it has rejected the proposal. 委员会已开过会,拒绝了这项建议。
5)--- What's this? --- It's a pen. —这是什么? —是一支钢笔。
6)--- Whose book is that? --- It's Mike's. —那是谁的书? —是迈克的。
7)Go and see who it is. 去看看是谁。
8)--- Who is making such a noise? —是谁发出这样的吵闹声?
--- It must be the children. —一定是孩子们。
3.虚义it无指代性,常用作没有具体意义的主语,出现于表示天气、气候、温度、时间、地点、距离等意义的句子中。如:
9)It is half past three now. 现在是三点半钟。
10)It is six miles to the nearest hospital from here. 这里离最近的医院也有六英里。
11)It was very cold; it snowed and grew dark.