This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urolithiasis, Subject name: Surgery
[{'content': 'Best investigation for ureteric stones is - \nSelect and explain. \nA. USG, B. CT, C. X-ray KUB, D. IVP', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. is \'b\' i.e., CT "Helical CT without oral or intravenous contrast is the preferred imaging modality for patients with renal colic or suspected urolithiasis" -- Smith\'s Urology', 'role': 'assistant'}]