情态动词

[例题]

1.It must have been around nine o'clock when I drove back home because it was already dark.

（当我开车回家时，肯定九点左右了，因为天已全黑了。）

2.He fell asleep immediately last night; he must have been very tired.

（昨天晚上他躺下就睡着了，他一定是很累了。）

3.You needn't have done all those calculations! We have a computer to do that sort of thing.

（你没有必要做这些计算！我们有计算机来做这种事情了。）

4.Mary couldn't have received my letter; otherwise she would have replied before now.

（Mary不可能收到我的信，不然她早就给我回信了。）

5.Comrade Li can't be in Beijing because I saw him in town only a few minutes ago.

（李同志不可能在北京，因为几分钟前我在镇里看见他。）

6.You promised her a letter; you should have written days ago.

（你答应过给她回信，你几天前就应该写了。）

7.Must I get everything ready before they come?

（我必须在他们来到之前就要做好一切准备吗？）

8.It's quite early. We needn't worry about the time.

（还早呢。我们用不着担心时间。）

9The road can be blocked[封堵].

（道路可能堵塞。）

[解析]情态动词must后面动词原形或完成式分别表示现在或过去情况的肯定猜测；情态动词can或could的否定形式后面跟动词原形或完成式分别表示对现在或过去情况的否定猜测；情态动词need的否定形式后面跟动词原形或完成式分别表示现在没有必要或过去没有必要做某事；should（或ought to）+“完成时”表示应该在过去做而没有做的动作。