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: ENT
Stridor is caused by - 
Select and explain. 
A. Obstruction of the airway below the level of larynx, B. Obstruction of the airway at the level of larynx, C. Obstruction of the airway above the level of larynx, D. Obstruction of the airway above the level of trachea
D: Obstruction of the airway above the level of trachea
Answer: D: Obstruction of the airway above the level of trachea 
Explanation: None