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3. strong, unpleasant and sometimes dangerous gas or smoke
4. useless repetition
6. a thick dirty cloud at ground level caused by pollutants reacting to sunlight
8. substances that carry harmful bacteria or toxins that can cause disease or death
9. existing everywhere
12. the part of the earth's atmosphere and surface in which animals and plants can live
13. ice caps Melting of ice in South and North
16. nearest dwarf planet to the solar system
17. waste Extremely toxic waste
18. a longing for something past

1. the geological process in which earthen materials are worn away and transported by natural forces such as wind or water.
2. a place where sky meets the water
3. extreme scarcity of food.
5. energy Direct radiant energy from the sun
7. renewable resources Can only be used once
8. the green colour component in the plant
10. an event causing great and usually sudden damage or suffering; a disaster.
11. a substance that has been linked to causing one or more types of cancer
14. a long period when there is little or no rain.
15. an enclosure within which something originates or develops