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
[{'content': 'Colour of O2 cylinder \nSelect and explain. \nA. Gray, B. Orange, C. Blue, D. Black & White', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Black & White', 'role': 'assistant'}]