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: Medicine
[{'content': 'Drug of choice in multple myeloma is - \nSelect and explain. \nA. Mechlorethamine, B. Vincristine, C. Vinblastine, D. Melphalan', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]