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
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? 
Select and explain. 
A. Ileocecal TB, B. Ca colon, C. Esophageal varices, D. Duodenal ulcer
D: Duodenal ulcer
Answer: D: Duodenal ulcer 
Explanation: None