An inter-breeding population of finches became separated geographically, forming two isolated groups. Each group then became subect to different selective pressures. One group was then introduced into the habitat of the other.
Which one of the following would determiner wheather they now formed two district species?

Options

A. They had been separated for more than three million years
B. They failed to produce fertile F.. hybrids
C. They showed marked differences in the shape of their beaks
D. Their plumage had become markedly different

Answer

B