The environment

3. the dying out of a species
7. energy that is replaced naturally and quickly
9. the process of treating things that have already been used so that they can be used again
12. the ability of a material to disintegrate (decompose) naturally by the action of living organisms
14. the fact of a country or city having too many people living in it
15. a substance that pollutes tha air, water or soil
17. waste gases that come out of a vehicle, an engine or a machine (2 words)
18. the gas that protects us from the UV rays

1. an animal's living area
2. the act of cutting down or burning the trees in an area
4. a thick forest in tropical parts of the world that has a lot of rain
5. a place where water flows over the edge of a steep, high cliff in hills or mountains, and falls into a pool below
6. a person who is interested in the natural environment and wants to improve and protect it
8. the protection of the natural environment
10. animals that are at risk of becoming extinct
11. the increase in temperature of the earth’s atmosphere that is caused by the increase of particular gases, especially carbon dioxide
13. the process of making air, water, soil, etc. dirty
16. a species that drinks mother's milk