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: Surgery
Sq. cell tumor of urinary bladder is due to ? 
Select and explain. 
A. Stone, B. Schistosomiasis, C. Chr. cystitis, D. All
D: All
Answer: D: All 
Explanation: Answer is 'a' i.e. Stone 'b' i.e. Schistosomiasis & 'c' i.e. Chronic cystitis