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 NADH, ATP, H2O, FAD+ or FADH2.

Glucose goes through three major pathways - Here, pathway A is glycolysis where 4 ATP are generated. Then the next pathway B is Krebs cycle where 8 ATP are generated after which, the last cycle is oxidative phosphorylation, where 12 ATP are generated. Thus, the correct answer is option (B).