1. 根据句意及首字母提示完成单词。

1. （1） The p of the world is becoming larger and larger.

3. （2） Too many cars on the roads cause traffic p.

5. （3） We know the i population is the biggest problem in the world.

7. （4） If there are too many people in the world, there won't be enough s for everyone.

9. （5） Planes make loud n when they take off.