challenge: What was the main difference in the aileron control system of the Stearman C2 compared to the C1?
  
  A. The C2 used a dual set of ailerons on both upper and lower wings
  B. The C2 used an aileron control system that actuated the single set ailerons via vertical push-pull rods connected to the upper wings
  C. The C2 used no ailerons at all
  D. The C2 used an aileron control system that actuated the single set ailerons on the upper wings via torque tubes internal to the upper wings
  Answer: 