使葡萄糖經糖解作用（glycolysis）後的產物直接進入克氏循環（Krebs cycle，亦稱citric acid cycle 或TCA cycle）的關鍵酵素為何？
succinate dehydrogenase complex
isocitrate dehydrogenase complex
pyruvate dehydrogenase complex
malate dehydrogenase complex
