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 _____.

下列有关生态系统稳定性的叙述，不正确的是[ ]

A．生态系统具有自我调节能力，这是生态系统稳定性的基础

B．生态系统内部结构与功能的协调，可以提高生态系统的稳定性

C．生物多样性对维持生态系统稳定性具有重要作用，体现了其间接价值

D．生态系统中的组成成分越多，食物网越复杂，生态系统的恢复力稳定性就越强