-The Figure Shows That Sickle Cell Allele Is Not Common

-The figure shows that sickle cell allele is not common in every region that malaria is present. Why not?

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.