一、助动词的作用

1.构成时态

He is singing.他在唱歌。

He has arrived.他已经到了。

Tomorrow will be the first day of autumn.明天是秋天的第一天。

2.构成语态

He was sent to England.他被派往英国。

The children have been having a lot of run.孩子们一直玩得很开心。

3.构成疑问句

Do you like college life？ 你喜欢大学生活吗？

Did you study French？ 你们学过法语吗？

Are the small animals kept in the cages？ 小动物都关在笼子里吗？

4.与not一起构成否定

I don’t like him.我不喜欢他。

If it should not snow tomorrow，we would not leave.明天不下雪，我们就不走。

5.强调谓语

I do love you.我真的喜欢你。

Do come to my birthday party.一定来参加我的生日宴会。

I did go there.我确实去那儿了。

6.构成倒装句

Never did I hear of such a thing.我从未听说过这样的事情。

Under no circumstances will I lend money to him.无论如何我也不会借钱给他。

Only when we begin our college life do we realize the importance of English.

只有在开始大学生活时我们才认识到英语的重要性。

7.替代实义动词

He made a mistake the other day and he did the same mistake again yesterday.

几天前他犯了一个错误，昨天他又犯了相同的错误。（did代替made）

— She loves roses most.她最爱玫瑰花了。

— So she does.她确实最爱玫瑰花。（does代替loves）