British Land Snails Are an Example of Disruptive Selection

Multiple Choice

British land snails are an example of disruptive selection.In the grassy fields,the light-banded snails escape bird predators.In the darker forest,the dark snails survive and the light-banded snails are eaten.As long as the snails continue to cruise across the British landscape mating at the same season,why doesn't this "disruptive selection" eventually lead to two separate species?

A) There is no reproductive isolation to prevent gene flow.
B) They are already two separate species,and the intermediate forms are hybrids.
C) The color forms are probably not genetically determined.
D) There must be some unknown factor producing an equal stabilizing selection "to hold the species together."
E) This will result in the formation of two species if given long enough time.