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 – \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: Single bubble appearance is seen in congenital hypertrophic pyloric stenosis.', 'role': 'assistant'}]