The correct answer is option a, that is, they were able to increase their productivity due to the popularity of tractors.
In comparison to early 1940 when one farmer was able to feed only 19 people, with the introduction of new technologies like motorized equipment, now the farmer is able to feed approximately 150 individuals. The farmers utilized technology to make progressions in generating more food for the developing world.
The modifications in equipment have created a huge influence on the manner by which the farmers were able to farm and grow food. In the past, the farmers were forced to do work in the field with hand or with the assistance of horse-drawn equipment. Due to this, it would take a longer time to complete the work, and thus, the farms were usually small.
Horses were not so fast, as they were animals, and would require some rest to recover. However, with the introduction of modernized equipment like tractors in the 1940s, farmers were able to generate more food in a shorter time period.