Answer:
D) The starch adapted flies and maltose adapted flies are not different species but a reproductive barrier is forming between the two populations.
Step-by-step explanation:
The preference of starch and maltose flies to mate with their own types indicates beginning of the formation of reproductive barrier between them. And the population is exhibiting divergent evolution. It would lead to formation of two different species after several generations. But right now, the barrier is not fully formed as indicated by presence of some mating between two types of flies.