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': 'The drug of choice for a patient with a combination of primary generalized tonic clonic seizure and absence seizures is: \nSelect and explain. \nA. Ethosuximide, B. Carbamazepine, C. Valproic acid, D. Phenytoin sodium', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]