Which Statement BEST Describes the Reproductive Isolation Between Populations of Rhagoletis

Which statement BEST describes the reproductive isolation between populations of Rhagoletis flies found on apple and hawthorn trees?

A) Hawthorn trees and apple trees grow in different areas, so the two populations do not encounter each other.
B) Male flies of one population cannot physically mate with females from the other population.
C) Hybrid offspring of the two populations are sterile.
D) Eggs laid by female flies mated with a male from the "wrong" population do not develop.
E) Apple-liking males are more likely to encounter apple-liking females than hawthorn-liking females.