69. During strenuous exercise, the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction in skeletal muscle must be reoxidized to NAD+ if glycolysis is to continue. The most important reaction involved in the reoxidation of NADH is _____(A) dihydroxyacetone phosphate → glycerol 3-phosphate (B) glucose 6-phosphate → fructose 6-phosphate (C) isocitrate → a-ketoglutarate (D) oxaloacetate → malate (E) pyruvate → lactate