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
The most useful investigation for profuse lower gastrointestinal bleeding is- 
Select and explain. 
A. Proctosigmoidoscopy, B. Colonoscopy, C. Double contrast barium enema, D. Selective arteriography
B: Colonoscopy
Answer: B: Colonoscopy 
Explanation: None