Which of the following statements stated below is precisely correct?
O A. Oxaloacetate is always regenerated during the Krebs cycle.
O B. The second substrate-level phosphorylation occurs during Krebs cycle.
O C. All the enzymes that catalyze the Krebs cycle are dehydrogenase.
O D. Answers A and B are the right answer choices for this question.
O E. Answers A, B, and C are the right answer choices for this question.