This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Functional Anatomy - Respiratory System, Subject name: Physiology
[{'content': 'Normal residual volume is - \nSelect and explain. \nA. 500ml, B. 1200ml, C. 3000ml, D. 2400ml', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 1200 ml", 'role': 'assistant'}]