The correct answer is C. He ran out of money.
Justinian I failed to regain all of the former provinces of old Roman Empire because he ran out of money. His once powerful army was weakened by the plague and the finances were down. He ran out of options.
Justinian I or Justinian the Great was the Eastern Roman Emperor from 527 to 565.
It was located in the middle of the Arabian Peninsula linking Yemen (which had major trading ports) and the Levant. It was also a pilgrimage site so there were always people there for worship which encouraged trade as well.
D or C us a hard question
They protect something about taxes and overseers