The sickle-cell allele is maintained in African populations even though when two

The sickle-cell allele is maintained in African populations even though when two sickle-cell alleles are inherited it can be fatal because 

 

   A. having two sickle-cell alleles makes the person immune to malaria.   
 

   B. having two non-sickle-cell alleles makes a person immune to malaria.   
 

   C. the sickle-cell allele is dominant.   
 

   D. having a non-sickle-cell allele and a sickle-cell allele makes the person more likely to be resistant to cystic fibrosis.   
 

   E. having a non-sickle-cell allele and a sickle-cell allele makes the person resistant to malaria.