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': 'Drug of choice for rapid cyclers in manic–depressive psychosis is : \nSelect and explain. \nA. Carbamazepine, B. Valproate, C. Phenytoin, D. Lithium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]