He must have been doing his homework then.

(3)(表示与说话人愿望相反及不耐烦)偏要

Just as I was hurrying to class, Mary must come, telling a

long story.

4. need

(1)"需要"，主要用于否定、疑问句。

You needn't do it at once.

(2)needn't have done,"过去不需要干而干了"：

You had enough time left. You needn't have hurried.

(3)特殊句型，"需要干某事"：

The tree needs (wants, requires) watering (to be watered).

5.dare，dared

(1)主要用于疑问、否定和条件句中：

How dared they do such a thing?

(2)可作实意动词：dare (to) do:

He didn't dare (to) go there.

6. shall, should

(1)shall用于第一、第三人称疑问句中，征求对方意见：

Shall I turn on the radio?

(2)shall用于第二、第三人称陈述句中，表示允诺、警告、命

令、决心等。

You shall fail if you don't take his advice.

Nothing shall stop us from carrying out this plan.

(3)should/ought to,"应该"：

You should work hard at your lessons.

(4)should(ought to) have done,"过去本来应该干某事而没干"；

should not have done"过去本来不应该干某事而干了",表示

委婉的批评：

You should have come earlier.

You shouldn't have told her about it.

You ought to have told me about that yesterday.

7. will, would

(1)用于疑问句，表示请求、邀请：

Will/Would you pass me the book?

(2)"愿意"：

If you will wait a little while, I'll call the manager.

(3)"总是"：

He will often sit up all night.

He would drop in on me on Sundays.

(4)用于否定句，表拒绝，尤指物：