This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': "Coenzyme used in Kreb's cycle ? \nSelect and explain. \nA. NAD, B. NADP, C. NADPH, D. NADH", 'role': 'user'}, {'content': "Answer: A \nExplanation: Niacin is used as coenzyme nicotinamide adenine dinucleotide (NAD') for transfer of hydrogen.", 'role': 'assistant'}]