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 _____.
