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: Radiology
[{'content': 'X-ray feature of pyloric stenosis is: March 2013 \nSelect and explain. \nA. Single bubble appearance, B. Double bubble appearance, C. Triple bubble appearance, D. Multiple bubble appearance', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. Single bubble appearance', 'role': 'assistant'}]