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.