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: Radiology
[{'content': 'The X-ray appearance of a CBD stone on cholangiography is: \nSelect and explain. \nA. Meniscus appearance, B. Eccentric occlusion, C. Sudden cut off, D. Smooth tapering', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Meniscus appearance', 'role': 'assistant'}]