Q: Fact 1: Bacteria in soil convert atmospheric nitrogen into a form usable by plants. Fact 2: Bacteria are single-celled organisms. Given the two facts above, what in soil converts atmospheric nitrogen into a form usable by plants?

Choose your answer from: 1. compound of hydrogen oxygen; 2. carbohydrates; 3. single-celled organisms; 4. excretory structures; 5. peachleaf willow; 6. members of their own species; 7. It helps them survive; 8. deoxyribonucleic acid;
A:
3.