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 to diagnose piles is - \nSelect and explain. \nA. Proctosigmoidoscopy, B. Barium enema, C. Ultrasound, D. Proctoscopy', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]