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: Pharmacology
[{'content': 'Ideal drug employed in the preoperative preparation for surgical excision of pheochromocytoma is: \nSelect and explain. \nA. Atenolol, B. Phenoxybenzamine, C. Reserpine, D. Clonidine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]