Answer:
B. Australia is isolated
Explanation:
They originated in South America and spread throughout the world, but due to competition on other continents, the other marsupials died out, while the ones on Australia lived.
One big reason for this is because individuals of the same species often have to fight over shared resources (this means shared food and shared environment).
Because they fight over a limited amount of space and food, competition between individuals within one species can be present and very tough.
On the other hand, having members of different species also possibly means different territories and different food sources. A lion has no quarrel with dolphins, while it can have a lot of fights with lions from different prides (large group of lions).
A. Nonnative species that are superior competitors
Formed by erosion created by seafloor spreading
RIVER DELTAS ARE formed by erosion created by seafloor spreading
NOT:
caused by the movement of tectonic plates areas of infertile, rocky soil