This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Local and Regional Anesthesia, Subject name: Anaesthesia
Pin index system for nitrous oxide: 
Select and explain. 
A. 1,6, B. 2,5, C. 3,5, D. 1,5
C: 3,5
Answer: C: 3,5 
Explanation: Ans: (c) 3,5Ref: Miller's Anaesthesia 7th ed. / 675GasColor CodePin index positionBodyShoulderOxygenBlackWhite2,5Nitrous oxideBlueBlue3, 5CO2GrayGray1,6HeliumBrownBrown2,5AirGreyWhite/black quartered1,5