This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
[{'content': 'Drug of choice for controlling severe pain in cancer patient is: \nSelect and explain. \nA. Morphine, B. Diclofenac, C. Ibuprofen, D. Codiene', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref: Katzung 10/e p449 Opioids like morphine can be used to treat severe pain associated with terminal cancers.', 'role': 'assistant'}]