How Did Pope Gregory I Seek to Protect the City

How did Pope Gregory I seek to protect the city of Rome?

A) He placed Rome under the authority and control of the emperors of the Eastern Roman Empire in Constantinople.
B) He overthrew the last Roman emperor and declared himself the leader of the Roman people, calling on all Romans to embrace Christianity to earn God's favor.
C) He adopted the model of the Roman imperial bureaucracy and applied it to the church in order to strengthen the importance of the Roman papacy to the church.
D) He made agreements with barbarian groups who had cut off Rome's food supply and reorganized church lands to increase production.