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_______.