The correct answer is: A group of wild horses is transported from Wyoming to a small desert island, previously without horses, off the coast of California. No additional horses reach the island thereafter.
Populations evolve to become distinct species and that is a process of creating new species or speciation. Allopatric speciation occurs when populations become isolated from the populations of the same species (gene flow between them doesn’t happen). In the example above, a group of wild horses is isolated from wild horses from Wyoming, and mostly likely will undergo genetic changes as a consequence of new environment. The exchange of genetic information between the two populations of wild horses will lead to reproductive isolation.