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: Radiology
[{'content': "Abdominal Ultra-sonography in a 3 year old boy shows a solid well circumscribed hypo-echoic renal mass. Most likely diagnosis is: \nSelect and explain. \nA. Wilm's tumor, B. Renal cell carcinoma, C. Mesoblastic nephroma, D. Oncocytoma", 'role': 'user'}, {'content': "Answer: A \nExplanation: Nephroblastoma (Wilm's tumour) is the commonest renal tumour in children and on USG appears a well circumscribed hypo echoic, solid mass. Ref: Differential Diagnosis in Abdominal Ultrasound By Bisset, 3rd Edition, 2008, Preview", 'role': 'assistant'}]