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
Urinary retention in child is most commonly caused by - 
Select and explain. 
A. Metal scab with ulceration, B. Post.urethral valve, C. Urethral stricture, D. Epispadias
B: Post.urethral valve
Answer: B: Post.urethral valve 
Explanation: None