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
Color of nitrous oxide cylinder is 
Select and explain. 
A. Black with white shoulders, B. White with black shoulders, C. Grey, D. Blue
D: Blue
Answer: D: Blue 
Explanation: Ans. d (Blue). (Ref. Short textbook of anesthesia by Ajay Yadav, 2nd ed., 21)Colour and pressure of cylindersSr. No.Anaesthetic gasColorPressure (bar) CyclopropaneOrange52.N2OBlue543.CO2Grey504.HalothaneAmber--5.EthyleneRed--6.HeliumBrown1377.O2Black body with white shoulder1378.Entonox (50%O2+50%N2O)Blue with white shoulder1379.AirGrey with white shoulder137Colour code for vaporizer of anaesthetic agents1. Red for /ralothane} 2. Orange for enflurane(HINT: ROPY HE-IS)3. Purple for isoflurane4. Yellow for sevoflurane