用情态动词can，may， must的适当形式填空。

1. —What _____ I do for you? 

    —I want some apples.

2. My father _____ ride a bike, but he drives a car.

3. You are ill, Tom. You _____ see a doctor.

4. Children _____ play football in the street.

5. If you are not careful, a car _____ hit you.

6. —_____ I come in? 

    —Come in, please.

7. A blind man _____ see anything.

8. Please ask the policeman, for he _____ know the way to

    the hospital, I'm sure.

9. —May I use your telephone? 

    —No, you _____.