用括号内所给动词的适当形式填空。

1. If you _________ (not be) careful enough when crossing the road, a car may hit you.

2. By the time he got home, his wife _________ (do) all the housework.

3. In the United States, lunch _________ (offer) to students for free at school.

4. The first step towards _________ (protect) the environment is to live a "low-carbon" lifestyle.

5. The day all the American basketball fans looked forward to _________ (come) at last.

6. While I _________ (sweep) the floor yesterday, the telephone rang.

7. Jack told me that they _________ to the USA from Shanghai by the end of next November. (return)

8. The disabled mustn't _________ (laugh) at by anybody.

9. The audience are required _________ (show) their tickets when they enter the cinema.

10. They _________ (eat) up all the food, but they still feel hungry.