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
Hamman's sign is seen in - 
Select and explain. 
A. Achalasia Cardia, B. Diffuse Oesophageal Spasm, C. Oesophageal perforation, D. Carcinoma Oesophagus
C: Oesophageal perforation
Answer: C: Oesophageal perforation 
Explanation: None