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': 'Which of the following is not given alone in a patient of pheochromocytoma ? \nSelect and explain. \nA. Atenolol, B. Prazosin, C. Nitroprusside, D. Metyrosine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]