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': 'A 65 years old patient of coronary artery disease was on Aspirin for 2 years. He now complains of black stools. Abdominal examination is normal. What is the most probable diagnosis? \nSelect and explain. \nA. Ileocecal TB, B. Ca colon, C. Esophageal varices, D. Duodenal ulcer', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]