Rates of sickle-cell disease and malaria are related because

a. they are genetic diseases, and people tend to carry both traits.
b. they are environmentally caused, and people in the same areas are likely to catch both.
c. sickle-cell disease carries a bacteria that causes malaria.
d. sickle-cell traits offer an immunity to malaria.
e. the medication that best treats malaria is deadly to those who have sickle-cell disease.

D