Believing the roman empire had grown too large for a single ruler, diocletian

a. withdrew armies from many of its borders, effectively shrinking the empire to a manageable size.
b. divided it into four units, each with its own ruler.
c. handed over power to the people, giving them control of the military for the first time.
d. divided it in half and appointed zeno as a ruler with equal power

i believe the answer is b, but i just want to make sure.