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
Hamman's sign is seen in: 
Select and explain. 
A. Pulmonary thromboembolism, B. Pulmonary atelectasis, C. Pneumomediastinum, D. Intralobar pulmonary sequestration
C: Pneumomediastinum
Answer: C: Pneumomediastinum 
Explanation: Hamman's sign is the Crunching sound heard with every heart beat because of heart beating against air fill.