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: Psychiatry
[{'content': 'Most commonly abused opioid - \nSelect and explain. \nA. Morphine, B. Diacetylmorphine, C. Oxycodine, D. Bupremorphine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Diacetylmorphine (heroin) is the most commonly abused opioid.', 'role': 'assistant'}]