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
Not a cause of acute anal pain 
Select and explain. 
A. Thrombosed hemorrhoids, B. Acute anal fissure, C. Fistula in ano, D. Perianal abscess
C: Fistula in ano
Answer: C: Fistula in ano 
Explanation: Ans. c. Fistula in ano