During aerobic respiration, molecular oxygen (O₂) is used for which of the following purposes?

• A. At the end of glycolysis to oxidize pyruvate
• B. At the end of the citric acid cycle to regenerate citric acid
• C. Between glycolysis and the citric acid cycle to split a carbon from pyruvate, producing CO₂
• D. As a source of O₂ in every reaction that produces CO₂
• E. At the end of the electron transport chain to accept electrons and form H₂O