| A | B |
|---|
| smog | a thick haze of smoke and chemicals |
| acid rain | chemicals in air pollution that mix with precipictation |
| greenhouse effect | build up of certain gases in the Earth's atmosphere that, like a greenhouse, retain the sun's warmth |
| crop rotation | changing what plants farmers plant in a field from year to year |
| deforestation | cutting down of forests without replanting new trees |
| conservation | careful use of resources to avoid wasting them |
| irrigation | process of collecting water and distributing it to crops |
| pesticide | powerful chemicals that kill crop-destroying insects |
| ecosystem | place shared by plants and animals that depend on one another for survival |
| biodiversity | variety of plants and animals living on the planet |
| layer | a thickness or fold |
| technique | a method of doing something |
| waste | use more of something than is necessary |
| distribute | give or send out; spread out over a large area |
