I would have thought that C is correct
Angle will Increase and then Decrease.
As you depart from Vy best rate, your angle of climb will increase as you progress towards Vx best angle. Remember that best climb is achievable with maximum excess thrust available. As you increase your AoA beyond that towards the critical AoA your speed reduces towards the stall speed you are progressively increase profile and induced drag and your thrust available is being progressively used up to balance the drag consequently is no longer excess.
Or in more simple terms Vy........Vx.........VS
Best Angle will be achievable at VX, any movement away from it either increase or decrease in speed will reduce your angle of climb.
Last edited by Rithalic; 13th Mar 2013 at 07:20.