Mark the statement if it correctly describes the beginning of the decline of the Roman Empire.
a. Incompetent rulers placed huge tax burdens on the Roman citizens.
b. The soldiers hired on the frontiers were not willing to go defend other parts of the empire.
c. Soldiers in the outer parts of the Roman Empire often supported local commanders instead of the emperor.
d. Regardless of the strength of the emperors, the Roman army was unable to hold back barbarian invasions from the south and west.