What/ who eventually filled the power vacuum in the eastern Frankish kingdom?

What/ who eventually filled the power vacuum in the eastern Frankish kingdom?
 
  A) The Hungarians were able secure leadership in the East, establishing their own empire.
  B) The Byzantines were able to expand into the Frankish territory and secure their authority.
  C) The nobles were desperate for strong leaders and all agreed the dukes of Saxony were the most powerful to defeat the Hungarians and became kings.
  D) The Slavs were able to secure a strong kingship and military to rule for centuries.
  E) The Capetian family was able to establish authority and drive the Hungarians out.