Answer: B. Population of a species become isolated from one another
Explanation: Speciation can be simply refered to as the development of new species over the span of Evolution.
Speciation includes the parting of a solitary developmental heredity into at least two hereditarily autonomous ancestries. This can be possible if this species are seperated from one another by a barrier such as River, Mountains etc, to the extent that each species evolve separately and distinctly and it becomes impossible for them to breed even though they were initially from the same specie lineage.