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': 'Investigation of choice for diagnosis of congenital hyperophic pylori stenosis: \nSelect and explain. \nA. USG, B. Barium meal, C. Barium meal follow through, D. CT scan with contrast', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. USG', 'role': 'assistant'}]