-The figure shows that sickle cell allele is not common in every region that malaria is present. Why are there differences in the presence of sickle cell alleles in these locations?

A) The sickle-cell allele only protects against some forms of malaria.
B) The sickle-cell allele is adaptive in only some races but not others.
C) The sickle-cell allele appeared by chance in certain populations and increased in frequency in those populations after it appeared.
D) The areas where sickle-cell and malaria overlap represent migration from the original population where sickle-cell arose.