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
Safety pin index for oxygen cylinder is 
Select and explain. 
A. 3,5, B. 1,5, C. 2,5, D. 1,4
C: 2,5
Answer: C: 2,5 
Explanation: None