1. 根据语境从方框中选择恰当的单词填空，有的需要变换形式。

pollute,   hopeless,   less,   enemy,   recycle

1. （1） The doctor advised me to eatmeat and more vegetables.
3. （2） These things can be.Don't burn them.
5. （3） If the water iswe can't get our drinking water from it.
7. （4） We tried to stop the fire from spreading, but we knew it was.
9. （5） Peter and Paul were friends in the past, but now they are.