This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
[{'content': 'In congenital hyperophic pyloric stenosis, the defect is in \nSelect and explain. \nA. Nerve fibres, B. Circular muscle fibres, C. Longitudinal muscle fibres, D. Mucosa', 'role': 'user'}, {'content': "Answer: B \nExplanation: Infantile Hyperophic Pyloric stenosis In HPS, hyperophy of circular muscle of pylorus results in constriction & obstruction of gastric outlet Accquired condition Incidence of 1 in 3000 to 4000 live bihs This condition is most common between the ages of 3-6 weeks Associated anomalies in 6-20% cases : Esophageal atresia, Hirschprung's disease, ARM and malrotation Ref: Sabiston 20th edition Pgno : 1869", 'role': 'assistant'}]