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': 'Rectal incontinence is due to involvement of \nSelect and explain. \nA. External anal sphincter, B. Internal anal sphincter, C. Ischiococcygeus, D. Pubococcygeus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Advanced tumours may cause faecal incontinence by invasion of the sphincters and, in women, anterior extension may result in anovaginal fistulation.Incontinence, especially if there has been inadveent damage to the underlying internal sphincter. Although uncommon, this is obviously a very serious problem that is difficult to treat Ref: Bailey & Love&;s Sho Practice of Surgery,E25,Page-1258,1269', 'role': 'assistant'}]