用所给词的适当形式填空。

1. Your present is in one of the _____ (box). Can you guess?

2. The students from America live on the _____ (nine) floor.

3. Houses in some cities now are much _____ (expensive) than before.

4. The clever girl could teach ______ (she) English when she was ten.

5. Chocolate is usually _____ (child) favorite food.

6. You may be _____ (worry) if you are in trouble and have no one to help you.

7. You won't know the result until you _____ (finish) reading the story.

8. They played so _____ (care) that they lost the football match.

9. Look, the Blacks _____ (plant) trees by the river.

10. Everyone should make a contribution to _____ (improve) the environment.