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': 'The following smooth muscle relaxants act by affecting calcium release except \nSelect and explain. \nA. Dantrolene, B. Prazosin, C. Metolazone, D. Nifedipine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Prazosin is alpha-1 blocker .', 'role': 'assistant'}]