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': 'Five-day self subsiding pain is diagnostic of - \nSelect and explain. \nA. Anal fissure, B. Fistul-in-ano, C. Thrombosed external hemorrhoids, D. Thrombosed internal hemorrhoids', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]