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 an active metabolite of another drug and is available as a separate drug for the treatment of angina ? \nSelect and explain. \nA. Isosorbide mononitrate, B. Isosorbide dinitrate, C. Nitroglycerine, D. Propranolol', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]