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': 'The diagnosis of congenital megacolon is confirmed by \nSelect and explain. \nA. Clinical features, B. Barium enema, C. Rectal biopsy, D. Recto-sigmoidoscopy', 'role': 'user'}, {'content': "Answer: C \nExplanation: -Biopsy from all three zones to study the ganglions and hyperophic nerve terminals in spasmodic segment. Staing from 2 cm above the dentate line, a full thickness rectal biopsy is ideal. * Barium enema is done to look for the extent of disease and three zones. Foley's catheter should not be used while doing barium enema in case of Hirschsprung's disease * Anorectal manometry--shows the absence of rectoanal reflex in Hirschsprung's disease, which is diagnostic. * Acetylcholine esterase staining shows hyperophied nerve bundles. ref:SRB &;s manual of surgery,ed 3,pg no-819", 'role': 'assistant'}]