Horses are able to mate with donkeys. Their offspring are animals known as mules. Mules are sterile, which means they cannot reproduce. Using this information, what can you conclude about horses and donkeys?
a. Horses and donkeys are the same species.
b. Horses and donkeys belong in different phyla.
c. Horses and donkeys are different subspecies of the same species.
d. Horses and donkeys are different species.