情态动词must和can

must和can是两个常用的情态动词，你知道它们的用法吗？请观察下面的例句，然后补全结论部分所缺的内容。

【例句】

1. You must be careful when you cross the road.

2. You mustn’t talk loudly in the library.

3. You can play after finishing your homework.

4. You can’t go home now.

【结论】

1. must意为“必须”，用于肯定句中，表示说话人的主观想法，即有必要或有义务去做某事，如例句1；must的否定形式是________，表示“禁止；不要”，语气比较强烈，如例句2。

2. can可以表示允许，意为“可以”，如例句3；can的否定形式是________，表示不允许，意为“不能；不要”，如例句4。

【拓展】

must还可以表示非常有把握的推测，意为“一定”。如：

That shop must be very good. Many people buy things there every day.

can’t还可以表示有把握的否定推测，意为“不可能”。如：

The boy can’t be Ben. He has gone back to his hometown.

【运用】根据句意从括号内选择适当的词语填空。

1. As students, we ________(can / must) study hard all the time.

2. You ________(can / can’t) make any noise because your sister is sleeping.

3. Mum, ________(can / must) I play basketball with my friends after I finish my homework?

4. You ________(must / mustn’t) play football in the street. It’s dangerous.

5. That man ________(can’t / mustn’t) be Mr Green. Mr Green is much shorter.

6. Our English teacher ________(can / must) be working now, because the light in her office is still on.

答案

【结论】mustn’t; can’t

【运用】1. must  2. can’t  3. can 4. mustn’t  5. can’t  6. must