In What Way Were the Abbasid Rulers Similar to the Roman

In what way were the Abbasid rulers similar to the Roman emperors?

A) Both increasingly relied upon diverse populations far from the imperial center to fill their armies.
B) Both effectively balanced the center and the periphery in imperial administration.
C) Both empires ultimately relied upon a single ethnicity for support.
D) Both located the center of religious devotion inside their imperial capital city.