Fact 1: Bacteria in soil convert atmospheric nitrogen into a form usable by plants.

Fact 2: More bacteria mean healthier soil.

Given the two facts above, answer the question "What allows soil to convert atmospheric nitrogen into a usable form by plants?" with the following options: 
- hydrogen and oxygen
 - diseased soil
 - peachleaf willow
 - bacteria-free soil
 - healthier soil
 - nutrients
 - virus filled soil
 - Cooking


 

     healthier soil    