A is heavier than C, B is lighter than D, F is heavier than E, D is heavier than A and F. Who is the heaviest?

C is heavier than A, B is lighter than D, F is heavier than E, D is heavier than A and F. Who is the heaviest?

C is heavier than A ⇒ A < C
B is lighter than D ⇒ B < D
F is heavier than E ⇒ E < F
D is heavier than A and F

∴ D is the heaviest.