Answer:
C. His army and finances were weakened by plague.
Step-by-step explanation:
Justinian I, also known as Justinian the great, was the emperor of the Eastern Roman empire, and he made strong efforts to re-conquer the old Roman empire, but his efforts were decimated by the plague that affected the bizantine empire, mainly the capital Constantinople, this weakened his armu and finances by the plague, so he couldn´t afford to continue reconquering the old Roman Empire.