Which Scenario Describes a Possible Route to Speciation by Habitat

Which scenario describes a possible route to speciation by habitat isolation?

A) The sperm of one species do not attach to the eggs of another species.
B) The cichlid fishes of Lake Malawi develop feeding specializations in rocky versus sandy habitats.
C) Mallard ducks and black ducks hybridize in areas where they overlap.
D) Pendant flowers are pollinated by hummingbirds, while upright flowers are pollinated by moths.
E) One population of deer breeds in winter, while another breeds in fall.