In What Ways Were Principles of Natural Selection Involved in the Increasing

In what ways were principles of natural selection involved in the increasing size of food grains like corn, wheat, and barley?

A) the fertilizer naturally favored the largest seeds
B) the key to improving grain size was weeding and increased sunlight
C) improvements to water supply from ditching, trenching, and irrigation enhanced the natural tendency of the largest grains to grow faster
D) natural selection was not involved because the processes involved humans selecting the best seeds