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: Pediatrics
[{'content': 'A child presented with intermittent episodes of left sided flank pain. Ultrasonography reveals a large hydronephrosis with dilated renal pelvis and coical thinning with a normal ureter. Kidney differential function was observed to be 19% which of the following is the best management: \nSelect and explain. \nA. Nephrectomy, B. Pyeloplasty, C. External Drainage, D. Endopylostomy', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Pyeloplasty', 'role': 'assistant'}]