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': 'In a 27 yr old male most common cause of a colovesical fistula would be - \nSelect and explain. \nA. Crohns disease, B. Ulcerative colitis, C. TB, D. Cancer colon', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]