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
The most useful investigation for profuse lower gastrointestinal bleeding is 
Select and explain. 
A. Proctosigmoidoscopy, B. Colonoscopy, C. Double contrast barium enema, D. Selective aeriolgraphy
B: Colonoscopy
Answer: B: Colonoscopy 
Explanation: .Indications for colonoscopy includes * Bleeding per rectum, resistant anaemia. * To take biopsies from different pas of the bowel. * To identify synchronous growths, ulcerative colitis. * To remove polyps. * When barium enema shows irregularity. * For therapy--colonoscopic polypectomy, dilatation of stricture colon, fulgaration. Contraindicated in Acute ulcerative colitis. ref:SRB&;s manual of surgery,ed 3,pg no 891