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: Surgery
[{'content': "Hamman's sign is seen in: \nSelect and explain. \nA. Pulmonary thromboembolism, B. Pulmonary atelectasis, C. Pneumomediastinum, D. Intralobar pulmonary sequestration", 'role': 'user'}, {'content': "Answer: C \nExplanation: Hamman's sign is the Crunching sound heard with every heart beat because of heart beating against air fill.", 'role': 'assistant'}]