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: Medicine
[{'content': 'The drug of choice for prompt relief of an ongoing attack of angina precipitated by exercise or emotional stress is: \nSelect and explain. \nA. Propranolol, B. Verapamil, C. Sublingual nitroglycerin, D. Sublingual nifedipine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]