6. There aren't many students taking part in the event.
7. They moved here two years ago.
8. If you don't turn unwanted lights off , you will waste a lot of electricity
9. Why don't we write about the three Rs?
10. It's fun to learn about recycling .
11 Reusable bags are more expensive than plastic bags
12. you shouldn't throw old clothes away.
13 Don't forget to turn the tap off when you are brushing your teeth
14 Unless we try to save our sources of energy , they will soon end.
15 Unless you keep your feet dry, you will catch a cold.
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