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: Forensic Medicine
[{'content': 'Which of these is not an opioid agonist: AIIMS 10 \nSelect and explain. \nA. Heroin, B. Ketamine, C. Methadone, D. Fentanyl', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Ketamine', 'role': 'assistant'}]