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.
