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
Squamous cell ca of urinary bladder is predisposed to by -a) Urolithiasisb) Persistent Urachusc) Schistosomiasisd) Polype) Smoking 
Select and explain. 
A. ac, B. bc, C. ad, D. b
A: ac
Answer: A: ac 
Explanation: Persistent urachus is a risk factor for adenocarcinoma of bladder.