Which of the following examples describes a postzygotic reproductive barrier that creates or enforces reproductive isolation?

W) Two closely-related species of garter snakes live in the same area, but one lives mainly in water while the other lives mainly on land

X) Two species of closely-related skunks have different mating seasons

Y) Two species of closely-related snails have morphological differences that prevent successful inter-species mating

Z) Two species of closely related equines may successfully mate to produce offspring, but the offspring is sterile
Z) TWO SPECIES OF CLOSELY RELATED EQUINES MAY SUCCESSFULLY