情態(tài)動詞

[例題]

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

（當我開車回家時，肯定九點左右了，因為天已全黑了。）

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

（昨天晚上他躺下就睡著了，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.

（你沒有必要做這些計算！我們有計算機來做這種事情了。）

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

（Mary不可能收到我的信，不然她早就給我回信了。）

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，因為幾分鐘前我在鎮(zhèn)里看見他。）

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

（你答應(yīng)過給她回信，你幾天前就應(yīng)該寫了。）

7.Must I get everything ready before they come?

（我必須在他們來到之前就要做好一切準備嗎？）

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

（還早呢。我們用不著擔心時間。）

9The road can be blocked[封堵].

（道路可能堵塞。）

[解析]情態(tài)動詞must后面動詞原形或完成式分別表示現(xiàn)在或過去情況的肯定猜測；情態(tài)動詞can或could的否定形式后面跟動詞原形或完成式分別表示對現(xiàn)在或過去情況的否定猜測；情態(tài)動詞need的否定形式后面跟動詞原形或完成式分別表示現(xiàn)在沒有必要或過去沒有必要做某事；should（或ought to）+“完成時”表示應(yīng)該在過去做而沒有做的動作。