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
Breath sound audible for more than------- seconds on auscultation over the trachea during forced expiration denotes significant airway obstruction: 
Select and explain. 
A. 2, B. 4, C. 6, D. 8
C: 6
Answer: C: 6 
Explanation: If breath sounds are audible for more than 6 seconds over trachea it denotes significant airway obstruction.