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
[{'content': 'Best investigation for carcinoma colon \nSelect and explain. \nA. Barium enema, B. Colonic biopsy, C. Clinical examination, D. Colonscopy', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]