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': 'Naloxone for opioid receptor acts as: \nSelect and explain. \nA. Pure agonist, B. Pure antagonist, C. Paial agonist, D. Agonist antagonist', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Naloxone is a pure antagonist and is preferred over older weak agonist-antagonist agents that had been used primarily as antagonists, eg, nalorphine and levallorphan. Ref: Katzung, 11th edition, Chapter 31.', 'role': 'assistant'}]