Respuesta :
Answer: Mechanical isolation
Explanation:
Mechanical isolation occurs when the reproductive structures of organism are not compatible. In this example, the coiling on the shells do not match, therefore the snails cannot reproduce.
Postzygotic isolation occurs when organisms have already fertilized an egg, but the offspring either died or was sterile.
Gametic isolation is when the gametes (egg cells and sperm cells) of organisms cannot produce offspring.
Behavioral isolation is a difference in reproductive behaviors such as mating calls that results in two organisms to refrain from reproducing with each other.
None of these apply except mechanical isolation.