This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: GIT and hepatobiliary system, Subject name: Radiology
[{'content': 'X-ray feature of pyloric stenosis is - \nSelect and explain. \nA. Single bubble appearance, B. Double bubble appearance, C. Triple bubble appearance, D. Multiple air fluid levels', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The plain XR will show a "single bubble" with air in a distended stomach. An elongated and narrowedpyloric canal (2-4cm in length) results in a "string" sign when a small amount of barium streaks through the pyloric canal', 'role': 'assistant'}]