情态动词+行为动词完成进行式(即情态动词+ have been + v-ing 形式)，表示推测或评论过去某动作是否正在进行或一直在进行。例如：

1)They should have been meeting to discuss the problem.

2)He may / might have been buying stamps in the post office when you saw him.

12.used to +v, be used to +v-ing和be used to +v

(1)used to +v意为“过去常常”，“过去一直”;be used to +v-ing / n(名词)意为“习惯于”;be used to +v意为“被用来(做某事)”。

(2)used to只表示过去，而be used to +v-ing / n可表示现在、过去或将来。例如：

1)He used to smoke. Now he doesn’t.

2)He’s quite used to hard work / working hard.

3)The knife is used to cut bread.

13.用作情态动词的其他短语

would rather, would sooner, would (just) as soon, had rather, had better, had sooner, can not but, may (just) as well等可用作情态动词。例如：

1)The soldier would sooner die than surrender.

2)The brave soldier would as soon die as yield to such an enemy.

3)I’d rather walk than take a bus.

4)If you don’t like to swim, you may just as well stay at home.

注：这些短语后一般直接跟动词原形.would (had) rather, would (had) sooner, would (just) as soon后可跟that 引导的从句，that 常省去，从句要用虚拟语气。对现在和将来的假设用过去时，对过去的假设用过去完成时。例如：

1)I would rather you came on Sunday.

2)I would sooner you hadn’t asked me to speak yesterday.

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