This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastro Intestinal System, Subject name: Pediatrics
[{'content': "A 10-year-old boy has complained for 1 month of intermittent epigastric pain that awakens him from sleep. He notes that eating food sometimes helps. He reports black stools during the prior week, and also admits that he has occasionally vomited frank blood. choose the best initial diagnostic step in the evaluation of the patient's apparent GI hemorrhage. \nSelect and explain. \nA. Abdominal series, B. Fiberoptic endoscopy, C. Apt test, D. Routine stool culture", 'role': 'user'}, {'content': 'Answer: B \nExplanation: PUD can result in hematemesis and melena, along with the typically epigastric abdominal pain. Children can have both chronic and acute blood loss associated with ulceration. Fiberoptic endoscopy is the diagnostic method of choice. An upper GI series can sometimes reveal an ulcer as well. While H pylori serum assays are available, they have limited usefulness in children.', 'role': 'assistant'}]