Sickle-Cell Anemia, a Blood Cell Mutation, Takes a Toll on Those

Sickle-cell anemia, a blood cell mutation, takes a toll on those afflicted, but is an example of a mutation that may also be useful because it

A) helps reduce the instance of melanoma, or skin cancer, in the tropics
B) provides a way for people to resist dangerous viruses like Ebola
C) offers health researchers a way to understand genetic differences in a closed population group
D) provides resistance to malaria in the tropics