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
Prismless enamel is 
Select and explain. 
A. Absent over cusp tips, B. Found in 70% of the permanent teeth., C. 25-30 micrometer thick, D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: None