If malaria were eradicated, what would happen to the sickle cell mutation?
a. heterozygosis would increase in the population
b. the frequency of the sickle cell mutation would increase in the population
c. the frequency of the sickle cell mutation would decrease in the population
d. no change would occur

The best answer is D.

Nothing would happen because the disease is genetic.  It is inherited and not acquired and its cause has absolutely nothing to do with malaria. The only thing that malaria does is that it can cause a dangerous medical condition called sickling crisis in a person with the sickle cell disease  which does not occur in people who do not have sickle cell disease even if they get infected with malaria.

The cause of sickle cell disease is  a mutation in the Beta chain of the protein molecule called hemoglobin. The mutation causes  the 6th amino acid called thymine  in the beta chain to be substituted with another  amino acid called valine. This change of a single amino acid causes the hemoglobin molecule to behave abnormally resulting in sicke cell disease.