When a horse mates with a donkey, it produces a mule. What evidence indicates that horses and donkeys are not the same species? A. The resulting mule, once it is mature, can produce offspring of its own. B. The mule can mate with a donkey to produce offspring. C. The mule and a horse would be able to mate and produce offspring. D. The mule that results from this mating, is sterile and not able to produce offspring of its own.