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: Anaesthesia
All except one affect minimum alveolar concentration 
Select and explain. 
A. Premedication, B. Age, C. Altitude, D. Drugs
C: Altitude
Answer: C: Altitude 
Explanation: Altitude does not affect MAC, since MAC is defined in terms of percentage of one atmosphere .