Which Best Explains How Australia Has Distinctive Organisms, Such as Marsupials

Which best explains how Australia has distinctive organisms, such as marsupials, that cannot be found anywhere else on Earth?

A) Australia has an unusual climate that has triggered natural selection.
B) There are fewer species of organisms in Australia than most continents.
C) Australia experienced a significantly slower rate of evolutionary change.
D) The predators of marsupials eliminated the populations in other locations.
E) Australia was separated and isolated from other land masses for a long period of time.