In Those Parts of Equatorial Africa Where the Malaria Parasite

Multiple Choice

In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
In the United States, the parasite that causes malaria is not present, but the sickle cell allele is present in many African-Americans whose ancestors were from equatorial Africa. Which of the following processes are most likely acting on the sickle-cell allele in the United States, and in equatorial Africa?

A) stabilizing selection in the United States; disruptive selection in equatorial Africa
B) disruptive selection in the United States; stabilizing selection in equatorial Africa
C) directional selection in the United States; disruptive selection in equatorial Africa
D) directional selection in the United States; stabilizing selection in equatorial Africa