The three boxes in this diagram represent the three major biosynthetic pathways in aerobic respiration. Arrows represent net reactants or products.
Arrows numbered 4,8 and 12 can all be :
FAD + or FADH2
NADH
ATP
H2O
As we discussed in concept
Pathway A is Glycolysis, B is Kreb's cycle and C is oxidative phosphorylation.