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': 'Drugs with high affinity can be used in : \nSelect and explain. \nA. High concentration., B. Low concentration., C. Moderate concentration., D. None.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Affinity is the ability of a drug to combine with the receptor.', 'role': 'assistant'}]