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': 'All of the following are known predesposing factors for cholangiocarcinoma except - \nSelect and explain. \nA. CBD stones, B. Clonorchis sinensis, C. Ulcerative colitis, D. Primary sclerosing cholangitis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]