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': 'Screening of colon cancer can be done by all except \nSelect and explain. \nA. Fecal occult blood, B. Colonoscopy, C. Flexible sigmoidoscopy, D. USG abdomen', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Faecal occult blood testing of people aged 60-69 years, followed by colonoscopy in those who test positive. A guaiac-based test is used, which detects peroxidase-like activity of faecal haematin. Studies have suggested a 15-20% reduction in colorectal cancer-specific moality in the screened population. Flexible sigmoidoscopy can also be used as the initial screening tool, with a similar reduction in colorectal cancer-specific moality.In FAP rectosigmoidoscopy is staed at 10- 12 years. In HNPCC colonoscopy is staed at 20-25 years.Ref: Bailey and love, page: 1262', 'role': 'assistant'}]