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 one of the following drug is contraindicated in acute myocardial infarction: \nSelect and explain. \nA. Morphine, B. Pentazocine, C. Nitroglycerin, D. Beta blockers', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]