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
Drug of choice for controlling severe pain in cancer patients is: 
Select and explain. 
A. Morphine, B. Diclofenac, C. Ibuprofen, D. Codiene
A: Morphine
Answer: A: Morphine 
Explanation: Morphine is a potent analgesic and relieves pain without loss of consciousness. Dull aching visceral pain is relieved better than sharp aching pain. Ref KD Tripathi 8th ed.