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 solid circumscribed hypoechnoic renal mass. Most likely diagnosis is - 
Select and explain. 
A. Wilm's tumor, B. Renal cell carcinoma, C. Mesoblastic nephroma, D. Oncocytoma
A: Wilm's tumor
Answer: A: Wilm's tumor 
Explanation: Amongst the given options only Wilms tumor is common at 3 years of age :-
	 Wilm's tumor                  → young children (mean 3 years)
	Mesoblastic nephroma     → < 1 year
	Renal cell carcinoma        → > 40 years
	Oncocytoma                    → 25-95 years (mean 65)