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: Surgery
[{'content': 'During investigation of hydronephrosis, isotope renogram is useful mainly in - \nSelect and explain. \nA. Detecting vesicoureteric reflux, B. Anatomical definition, C. Distinguishing between non-obstructed system, D. Identifying ectopic kidney tissue', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]