Which of the Following Observations Would Constitute Conclusive Evidence That

Which of the following observations would constitute conclusive evidence that two overlapping populations that had been geographically separated have not diverged into distinct species?

A) Matings between members of the two populations produce viable hybrids.
B) A stable hybrid zone exists where their ranges overlap.
C) Interbreeding is common between members of the two populations.
D) All of the above
E) None of the above