challenge: What event in 235 led to the rise of Maximinus Thrax as Emperor?
  
  A. The defeat of Maximinus Thrax by Emperor Alexander Severus in a battle
  B. The resignation of Emperor Alexander Severus and the nomination of Maximinus Thrax as his successor
  C. The assassination of Emperor Alexander Severus and his mother Julia Avita Mamaea by mutinous troops
  D. The death of Emperor Alexander Severus's mother, Julia Avita Mamaea, due to natural causes
  Answer: 