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: Medicine
[{'content': "Hamman's sign is seen in - \nSelect and explain. \nA. Achalasia Cardia, B. Diffuse Oesophageal Spasm, C. Oesophageal perforation, D. Carcinoma Oesophagus", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]