This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hemodynamics, Subject name: Pathology
[{'content': 'A 33-year-old woman presents with black stools. Laboratory studies demonstrate a hypochromic, microcytic anemia. Upper GI endoscopy reveals a duodenal ulcer. Which of the following best describes the stools in this patient with peptic ulcer disease? \nSelect and explain. \nA. Hematemesis, B. Hematobilia, C. Hematochezia, D. Melena', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Melena (black stool) is a symptom of upper gastrointestinal bleeding. Blood from ruptured esophageal varices or a peptic ulcer is partially digested by hydrochloric acid. Hemoglobin is transformed into a black pigment (hematin), which imparts a typical "coffee-grounds" color to the stool. Hematemesis (choice A) is vomiting of blood. Hematobilia (choice B) is bleeding into the biliary passages, as a complication of trauma or neoplasia. Hematochezia (choice C) is passage of bloody stools caused by lower gastrointestinal hemorrhage. Steatorrhea (choice E) is passage of fatty stools caused by pancreatic disease and malabsorption.Diagnosis: Peptic ulcer disease', 'role': 'assistant'}]