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: Physiology
[{'content': 'Normal residual volume is ? \nSelect and explain. \nA. 500 ml, B. 12 00 ml, C. 3000 ml, D. 2400 ml', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is'b'i.e., 1200 ml(Ref: Ganong 24e/e p.629)", 'role': 'assistant'}]