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: Dental
[{'content': 'Which of the following is not a natural abrasive \nSelect and explain. \nA. Arkansas stone, B. Pumice, C. Tripoli, D. Rouge', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]