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 _______ drive 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(盲人)._______ 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_______.