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: Pharmacology
Pin index of oxygen is which one of the following : 
Select and explain. 
A. 2, 5, B. 3, 5, C. 1, 5, D. 3, 6
A: 2, 5
Answer: A: 2, 5 
Explanation: None