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: Surgery
[{'content': 'Best treatment modality for common bile duct stone is - \nSelect and explain. \nA. Endoscopic sphincterotomy, B. Observation, C. Chenodeoxycholic acid, D. Percutaneous removal', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]