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': 'Gum hypertrophy is an adverse effect of the following drug when used at therapeutic levels : \nSelect and explain. \nA. Phenobarbitone, B. Phenytoin, C. Carbamazepine, D. Sodium valproate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]