Answer: The correct answer is-
When members from a separated populations do not reproduce with each other, they will become two different species.
According to the biological species concept of Ernst Mayor, organisms that are capable of interbreeding and producing viable and fertile offsprings belong to one species.
In this question a population has become separated and the members from the separated population do not reproduce with each other. This means that the population has become reproductively isolated and no gene flow occurs between them.
Thus, they will become two different species.