After World War II, most American farmers:
a-replaced polyculture with monoculture, that is, they went from raising a variety of livestock, and growing a variety of crops, to focusing on a single cash crop
b-replaced monoculture with polyculture, that is, they went from focusing on a single cash crop to raising a variety of livestock, and growing a variety of crops
c-began experimenting with organic methods of crop production
d-substantially reduced their level of dependence on chemical fertilizers