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
Best investigation for carcinoma colon 
Select and explain. 
A. Barium enema, B. Colonic biopsy, C. Clinical examination, D. Colonscopy
D: Colonscopy
Answer: D: Colonscopy 
Explanation: None