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: Medicine
[{'content': 'A young patient presenting with massive hematemesis was found to have splenomegaly. In this case the most likely source of bleeding is - \nSelect and explain. \nA. Duodenal ulcer, B. Esophageal varices, C. Erosive mucosal disease, D. Gastric ulcer', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]