Answer:
B) crop rotation
Step-by-step explanation:
In the early 1900's, George Wasington Carver was a chemist who made important discoveries in the field of agricultures thereby manufacturing important tools (inventions). Part of his major works which was on agriculture contributed immensenly to the growth of farming activities by farmers and their feeding lifesyles.
To the farmers, he was able to notice that there is a significant loss of soil nutrient after farming activities leading to them adopting fallow methods to replenish it. In order to solve this issue, he suggested to the farmers to adopt the crop rotation method in the farming as a result of the benefits to gain from it.
This theory by him was as a result of the discovery that he made when a deep rooted plant is planted next to a shallow rooted plant. This is to replensih nitrogen to the soil of those farmland through systematic crop rotation.