This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anaesthesia, Subject name: Anaesthesia
[{'content': 'The most potent synthetic opioid is \nSelect and explain. \nA. Remifentanil, B. Sufentanil, C. Alfentanil, D. Fentanyl', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Sufentanil has a high affinity for the mu receptor, higher than that of any other opioid.', 'role': 'assistant'}]