1. (2016·衢州) 用方框中所给单词的适当形式填空，每题仅用一次，每空限填一词。

pollute     proper    six     powerful      they

1. （1） Schools should do something to help students protect .

3. （2） If a river is , farmers can't use the water for their crops.
   

5. （3） The Internet is more  than books. It is influencing our lives a lot.

7. （4） The students who are good at writing can always use words .

9. （5） Children usually attend a primary school at the age of  in China.