This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sympathetic System, Subject name: Pharmacology
[{'content': 'Nonselective reversible a receptor blocker among the following is \nSelect and explain. \nA. Phenoxybenzamine, B. Phentolamine, C. Prazosin, D. Terazosin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Nonselective irreversible a receptor blocker Phenoxybenzamine Nonselective reversible a receptor blocker Phentolamine Selective a receptor blocker Prazosin Terazosin Doxazosin', 'role': 'assistant'}]