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
The first and most important step in management of a case of trauma is: 
Select and explain. 
A. Supply large amount of oxygen, B. Start intravenous infusion, C. Clearing the airway, D. Call ambulance
C: Clearing the airway
Answer: C: Clearing the airway 
Explanation: "Upon initial evaluation, ascertaining patency of the airway is of highest priority."