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: Pathology
[{'content': "Fistula is most common in - \nSelect and explain. \nA. Crohn's disease, B. Ulcerative colitis, C. Infective entero colitis, D. Coeliac sprue", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]