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 ethylene cylinder is: \nSelect and explain. \nA. Blue, B. Grey, C. Orange, D. Purple', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Purple', 'role': 'assistant'}]