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': 'Therapeutic level of phenytoin is : \nSelect and explain. \nA. 0–9 mg/ml, B. 10–19 mg/ml, C. 20–29 mg/ml, D. 30–39 mg/ ml', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]