用括号内所给单词的适当形式填空。

1. This toy Is not____(suit) for young children.

2. There____(use) to be a lot of birds here, but now we can hardly see them.

3. The heavy rain stopped the visitors____  (climb) the mountain.

4. They often collect waste paper and bottles for____(recycle) to protect the environment,

5.--What're they doing?

   --They're____ (wait) for a bus.