After the last major ice age, sea levels around the world rose. As they did, the rising waters divided what was once a single island in the North Sea into two different islands. A population of rabbits was split between the two islands. Ten thousand years passed with no contact between the two rabbit groups. In recent times, a scientist attempted to breed individuals from the two groups, but he was unsuccessful in doing so. Why were rabbits from the two groups unable to produce offspring together?

A.
The groups were adapted to very different climates.
B.
The groups were not able to recognize each other.
C.
The groups belonged to different breeds of rabbits.
D.
The groups had evolved into separate species.

D. The groups had evolved into separate species.