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': 'The most common cause of suppurative cholangitis is - \nSelect and explain. \nA. Stone in common bile duct, B. Cancer of the ampulla of vater, C. Choledochal cyst, D. Empyema of gall bladder', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]