Islands Are Well Known for Having Many Endemic Species Species

Islands are well known for having many endemic species species that are unique to that location.What is a likely explanation for this pattern?

A) Colonizers encounter fewer competitors on an island,so they can diversify.
B) Islands are more complex habitats than continents are,so they have more niches for specialization.
C) Humans bring partly or fully domesticated species with them when they arrive on islands.
D) The type of organism that is a good colonizer has more than the average amount of genetic variability,so it's more likely to speciate.
E) Islands are often distant from mainlands and therefore island species cannot emigrate to other areas.