The Island of Madagascar, Off the Southern African Coast, Has

The island of Madagascar, off the southern African coast, has a highly unique endemic biota.Roughly 170 million years ago, Madagascar was landlocked in the middle of the supercontinent Gondwana.Gondwana eventually split by continental drift, forming Africa, South America, India, Australia, and Antarctica.For the past 88 million years, Madagascar has been isolated, but some new species can still reach the island from the coast of Africa.This suggests that the evolution of Madagascar's unique biota is

A) due entirely to dispersal resulting from immigration.
B) due entirely to vicariance resulting from continental drift.
C) due only to genetic factors, with no environmental input.
D) due to chance development of new species assemblages on the island.
E) due to both vicariance from continental drift and dispersal by immigration.