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: Radiology
[{'content': 'Pneumothorax is best demonstrated by taking a radiograph, with patient in: \nSelect and explain. \nA. Mid inspiration, B. End expiration, C. Full inspiration, D. Supine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. End expiration', 'role': 'assistant'}]