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
All enamel walls of a cavity preparation must consist of full length enamel rods on 
Select and explain. 
A. Affected enamel, B. Affected dentin, C. Sound enamel, D. Sound dentin
D: Sound dentin
Answer: D: Sound dentin 
Explanation: None