There is a great deal of regional variation in the frequency of many human ailments, up to 500 percent variation per 100,000 between different areas in the numbers of pneumonia, skin cancer, tuberculosis, and rheumatoid arthritis occurances.
To support a conclusion that much of the variation is due to the genetic makeup and distribution of the population, it would be most important to establish which of the following?
(A) The variation is unrelated to disease-incidence influencing factors outside of the genetic makeup of various regional populations.
(B) A committee in each region researches the medical records of people in that region and cross-references it with their place of residence for their entire lifetime to determine whether these people are native to the region.
(C) There are several categories of disease (other than pneumonia, skin cancer, tuberculosis, and rheumatoid arthritis) that are often the result of genetic factors.
(D) For certain ailments it is difficult to determine after people have recovered whether the ailment was caused by genetic factors or other factors.
(E) Pneumonia, skin cancer, tuberculosis, and rheumatoid arthritis are representative of ailments in general with respect to how often they are the result of genetic factors.