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: Unknown
[{'content': 'Anaphylaxis is caused by- \nSelect and explain. \nA. N2O, B. Althesin, C. Halothane, D. Propofol', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (Refer: Morgan and Mikhail’s Clinical Anaesthesiology, 5th edition)\nAlthesin\n\nAlthesis is a neurosteroid\nIt was used as a parenteral anaesthetic\nIt was withdrawn from the market because of several severe anaphylactic reactions', 'role': 'assistant'}]