Why Is the HbS Mutation So Prevalent in Africa and Other

Why is the HbS mutation so prevalent in Africa and other tropical regions?

A) The oxygen binds with greater affinity to the proximal histidine residue of HbS.
B) Bonding of carbon dioxide to HbS molecules increases the binding of oxygen.
C) Hemoglobin binds more oxygen with the reduction of the hemoglobin S chain.
D) Hemoglobin binds more oxygen with aggregations of α chains found in sickle-cell hemoglobin.
E) People with sickle-cell trait are resistant to malaria, increasing the prevalence of the HbS allele.