This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthetic equipments, Subject name: Anaesthesia
Safety pin index for oxygen cylinder is- 
Select and explain. 
A. 2,5, B. 3,5, C. 1,5, D. 1,4
A: 2,5
Answer: A: 2,5 
Explanation: Safety pin index cylinder for oxygen is 2 , 5 . It is done to prevent wrong fitting of cylinders .