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': 'Plasma drug monitoring is done for: \nSelect and explain. \nA. Drug with high safety margin, B. Drug with low safety margin, C. Drug with high therapeutic index, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]