This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Amino acid responsible for buffering action of Hemoglobin \nSelect and explain. \nA. Histidine, B. Arginine, C. Valine, D. Lysine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The second buffer system is provided by the dissociation of the imidazole groups of the histidine residues in hemoglobin.Ref: Ganong&;s Review of medical physiology 25th edition. Page: 644', 'role': 'assistant'}]