Which Scenario Describes Allopatric Speciation

Which scenario describes allopatric speciation?

A) A population of squirrels is separated by the Grand Canyon. The two subpopulations evolve into two distinct species.
B) A tetraploid plant species evolves from a diploid ancestor. Both the tetraploid and diploid species are found in the same habitat.
C) One population breeds in the fall; another population breeds in the spring.
D) A male horse and a female donkey mate, producing a sterile hinny.