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: Surgery
[{'content': 'Rectal incontinence is due to involvement of :a) External anal sphincterb) Internal anal sphincterc) Ischiococcygeusd) Pubococcygeus \nSelect and explain. \nA. acd, B. bcd, C. abc, D. abd', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Rectal continence depends solely on the anorectal ring and any damage to this ring results in rectal incontinence.\nThe anorectal ring is a muscular ring present at the anorectal junction, and formed by the fusion of -\n\nPuborectalis (a part of pubococcygeus which in turn is a part of levator ani)\nDeep external anal sphincter\nInternal anal sphincter\n\nThe puborectalis muscle appears to be the most important muscle for maintaining fecal continence.', 'role': 'assistant'}]