Diffusion of Corn as a Food for Both Animals and Humans

Diffusion of corn as a food for both animals and humans:

A) Occurred very slowly because there was little trade or contact within the Americas.
B) Has permanently altered global agricultural patterns over the past 300 years.
C) Has been extensive, but outside the Americas, it is primarily a trade item because it requires very specific soils and climate.
D) Is of limited economic value because other, more easily grown substances work as well and are less expensive.