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': 'The most important feature of the following opioid analgesic is high oral parenteral activity ratio (1:2): \nSelect and explain. \nA. Morphine, B. Oxymorphine, C. Methadone, D. Diacetylmorphine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]