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
[{'content': 'Not a cause of acute anal pain is: \nSelect and explain. \nA. Perianal abscess, B. Thrombosed hemorrhoids, C. Acute anal fissure, D. Fistual in ano', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]