In the Galapagos Islands,which of the Following Would Have Prevented

In the Galapagos Islands,which of the following would have prevented the evolution of the many different species of finches?

A) the availability of different food sources on each island
B) the appearance of a disease that kills off many finches
C) introduction of predators preferentially consuming ground finches
D) frequent migration of finches between the islands
E) dramatic reduction in population due to drought