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
Therapeutic index is an assessment of: 
Select and explain. 
A. Potency of a drug, B. Onset of action, C. Duration of action, D. Margin of safety
D: Margin of safety
Answer: D: Margin of safety 
Explanation: None