Which of the Following Situations Provides the Best Example of 'Balanced

Which of the following situations provides the best example of 'balanced polymorphism'?

A) Dark and light colored moths were distributed equally in industrial England.
B) The sickle cell trait is selected for at a rate high enough to confer protection from malaria but low enough to keep death rates from sickle cell anemia in check.
C) Lactose tolerance in some populations is balanced out by lactose intolerance in others.
D) The hemoglobin allele that offers protection from both malaria and sickle cell anemia exists in a balance with a hemoglobin allele that offers no protection.
E) Moth wing color alleles co-exist at rates that go up and down over time depending on which environmental pressures are more active.