This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
[{'content': 'Residual volume is the volume of air in lung after \nSelect and explain. \nA. Maximal inspiration, B. Maximal expiration, C. Normal inspiration, D. Normal Expiration', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The air left in the lungs after a maximal expiratory effo is the residual volume.Ref: Ganong review of medical physiology 23rd edition Page no: 593', 'role': 'assistant'}]