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': 'A patient presents with acute renal failure with normal ultrasound abdomen report. Next most useful investigation is - \nSelect and explain. \nA. Intravenous pyelography, B. DTPA scan, C. Retrograde pyelography, D. X-ray abdomen and CT scan.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]