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 index is an assessment of: \nSelect and explain. \nA. Potency of a drug, B. Onset of action, C. Duration of action, D. Margin of safety', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]