As scientists have developed more productive crop varieties, farmers have switched from growing many traditional varieties to new high-yield varieties. For example, in Peru, the Indians once grew 500 native varieties of potatoes. That number has been reduced to about twenty major potato varieties, worldwide. Why is it potentially dangerous to reduce the number of crop species in potatoes? A) It reduces the variety of crops available for human diets. B) It requires a larger investment than small farmers can make. C) It makes the overall crop more susceptible to pests or disease. D) It could reduce or cause the extinction of some predatory insects.