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': 'Prismless enamel is \nSelect and explain. \nA. Absent over cusp tips, B. Found in 70% of the permanent teeth., C. 25-30 micrometer thick, D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]