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': 'Which of the following is 100 times more potent than morphine? \nSelect and explain. \nA. Pethidine, B. Fentanyl, C. Pentazocin, D. Meperidine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Fentanyl is 100 times more potent than morphine. Pethidine is 1/10th as potent as morphine. Ref KD Tripathi 8th ed.', 'role': 'assistant'}]