This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
[{'content': 'Opioid agonist are A/E - \nSelect and explain. \nA. Morphine, B. Codeine, C. Ketamine, D. Methadone', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Ketamine", 'role': 'assistant'}]