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': 'Stages of anaesthesia were described by Guedel with \nSelect and explain. \nA. Ether, B. Chloroform, C. N20, D. Halothane', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ether', 'role': 'assistant'}]