This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney and ureter, Subject name: Surgery
[{'content': 'Most common renal tumor in neonatal period: \nSelect and explain. \nA. Renal cyst, B. Congenital mesoblastic nephroma, C. Neuroblastoma, D. Nephroblastoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: "Although congenital mesoblastic nephroma (CMN) is a rare benign congenital renal tumor it is the most common solid renal tumor in the neonatal period."', 'role': 'assistant'}]