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': 'An appendicular fistula is least likely to heal if - \nSelect and explain. \nA. The stump was sutured with vicryl, B. There is stenosis/narrowing of the sigmoid colon, C. Superadded infection, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Unrelieved obstruction of tube distal to fistula is a cause of persistence of fistula.', 'role': 'assistant'}]