A Young Dog Has Never Had Much Energy

A young dog has never had much energy. He is brought to a veterinarian for help, and she decides to conduct several diagnostic tests. She discovers that the dog's mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of the dog's condition?

A) His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
B) His cells cannot move NADH from glycolysis into the mitochondria.
C) His cells lack the enzyme in glycolysis that forms pyruvate.
D) His cells have a defective electron transport chain, so glucose is metabolised to lactate instead of to acetyl CoA.