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, there are about 500 native varieties of potatoes that Indians once grew. This has been reduced to about 20 genetically improved potato varieties worldwide.

Besides the number of varieties of potatoes being reduced, what else is reduced by this practice?

A. the potato gene pool
B. human dietary choices
C. types of soil nutrients
D. food chains that include potatoes