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: Medicine
[{'content': 'Klatskin tumour is tumour - \nSelect and explain. \nA. At the juncture of cystic duct and bile duct, B. At bile duct, C. At ampulla of vater, D. At the junction of the bile duct', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]