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': 'Efficacy of a drug refers to: \nSelect and explain. \nA. Affinity of drug to bind to receptors, B. Affinity of drug that binds to receptors and activates it, C. Dose that requires to produce response, D. Maximum response a drug can produce', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]