A. Either flank them with heavy cavalry and disrupt their formation or use missile forces to push them into testudo and them target them with artillery.
B. Combination of disciplined infantry (because Dothraki don’t flank infantry) to pin them in place and then heavy cavalry to encircle and counter-charge them, making sure to always wheel back to the line.
C. Assymetric warfare combined with attempts to bring the dragons down either by artillery, poison, assault on a downed dragon.
D. This one is tricky. @warsofasoiaf, any thoughts?