How Did Charlemagne Attempt to Maintain Control Over Local Authorities

How did Charlemagne attempt to maintain control over local authorities?

A) He required the eldest sons of local officials to live at court, where they could be watched and threatened if their fathers proved disloyal.
B) He appointed officials who checked up on local officials and held courts to handle judicial and financial issues.
C) He frequently traveled his domain, arriving at the homes of local officials without warning.
D) He frequently rotated local officials among different localities to prevent the officials from forming bonds with the local people.