1. 用所给词的适当形式填空

1. （1） This is a difficult (society) problem to solve.

3. （2） It's a (an) (usual) experience, and few people have chances to do it.

5. （3） Would you like (collect) shells with me?

7. （4） He was moving (rapid) around the room.

9. （5） We (learn) English last night.