In this Paradox question, we want to explain why these people continued to grow corn as their staple grain even though corn is less nutritious than the grains they used to grow and led to health problems “soon after” they established corn as their staple grain.
(E) provides a reason why. They realized that corn + other foods actually improved their health. While they had health problems “soon after” they started growing corn, a few years later they learned that corn plus other foods could make them more healthy.
(C) makes the paradox even stranger. It says these people *didn’t* raise animals that could provide meat or milk that would make their diets healthier. By removing one source of nutrients, (C) makes corn — which we’re told isn’t that healthy by itself — a large part of the people’s diets. If they were eating a lot of corn, they would probably experience a lot of health problems, makign it strange that they would rely on corn as their staple crop.