Hmmm. I would have throught primary must mean under direct control of the pilot (i.e. not A/P) and directly affects the attitude of the a/c. D is interesting because of the word "about". I would have throught that the throttle is a primary control
along the longitudinal axis, as that is not mentioned then it is strictly incorrect. I wouldn't consider flaps a primary control because they are intended to change the flight characteristic for very specific reasons. Faced with Roll and Pitch or Ailerons and Rudder I would say that Rudder is least important so I would answer A or D. Being somewhat concerned that I am reading too much into D I may settle on D after flipping a coin.
