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
Abdominal Ultra-sonography in a 3 year old boy show a soild circumscribed hypoechnoic renal mass. Most likely diagnosis is- 
Select and explain. 
A. Wilm's tumor, B. Renal cell carcinoma, C. Mesoblastic nephroma, D. Onceocytoma
A: Wilm's tumor
Answer: A: Wilm's tumor 
Explanation: A i.e. Wilm's tumor