A certain genetic mutation is found with a high frequency in populations of humans living in places that experienced a deadly disease in the past. This same mutation is rare in places that have no history of the disease. Based on how genes work, this data best supports which of the following explanations?
a.The genetic mutation was present in all populations but did not get passed on in places where humans did not contract the disease.
b.This genetic mutation codes for the production of a protein that provides resistance to the disease.
c.The disease causes the genetic material of humans to mutate just before it causes their disease.
d.Humans with this mutation develop this disease and then spread it to other humans without the mutation.