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': 'Breath sound audible for more than------- seconds on auscultation over the trachea during forced expiration denotes significant airway obstruction: \nSelect and explain. \nA. 2, B. 4, C. 6, D. 8', 'role': 'user'}, {'content': 'Answer: C \nExplanation: If breath sounds are audible for more than 6 seconds over trachea it denotes significant airway obstruction.', 'role': 'assistant'}]