challenge: According to Dio Cassius, why did Emperor Caracalla have the Quadi king Gaiobomarus executed?
  
  A. For refusing to meet with Caracalla
  B. For leading a successful raid into Pannonia
  C. For forming an alliance with the Marcomanni
  D. As a result of Caracalla's deceit, claiming the Germans' recklessness and greed could not be conquered by force
  Answer: 