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': 'Ultrasonogram is not useful in: \nSelect and explain. \nA. CBD stones at the distal end of the CBD, B. Breast cyst, C. Ascites, D. Full bladder', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. CBD stones at the distal end of the CBD', 'role': 'assistant'}]