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

A) the potato gene pool

Explanation:

There are used to be 500 varieties of potato, but now its only 20 varieties of potato. The number of potato kinds if reduce to 1/25 of it used to be. This means the gene/allele that makes the 475 varieties of potato is gone. The gene pool of 20 varieties should be lower than 500 varieties.

Opposed to natural selection, this event should be artificial selection. Humans only breed potatoes that can yield more harvest, potatoes that more delicious, or any trait that benefits humanity.

i think the answer is a, hope this is right, that would be my best guess.