Carriers of Cystic Fibrosis Have Some Protection Against Intestinal Infections

Carriers of cystic fibrosis have some protection against intestinal infections such as cholera.However,people with two copies of the cystic fibrosis allele develop a life-threatening disease.The mutant allele is very common in people of northern European descent because of

A) disruptive selection.
B) directional selection.
C) artificial selection.
D) sexual selection.
E) stabilizing selection.