| __ | 1. | Animals eat carbon and then | | A. | with plants breathing in carbon dioxide. |
| __ | 2. | Animals get carbon by | | B. | eating plants or other animals. |
| __ | 3. | Animals use carbon by | | C. | gas in the atmosphere. |
| __ | 4. | Carbon can be trapped | | D. | burning it as fuel. |
| __ | 5. | Humans add carbon to the cycle | | E. | by using lots of fertilizers. |
| __ | 6. | Humans pollute with nitrogen | | F. | with bacteria on plant roots. |
| __ | 7. | Nitrogen exists mainly as | | G. | breathe out carbon dioxide. |
| __ | 8. | Nitrogen is released as gas | | H. | by decomposers. |
| __ | 9. | The carbon cycle begins | | I. | by plants and animals dying and being deeply buried. |
| __ | 10. | The nitrogen cycle begins | | J. | by burning oil and coal. |