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
Floor of class II cavity for amalgam restoration, occlusally should be: 
Select and explain. 
A. In enamel, B. In dentin, C. In DEJ, D. Just above the roof of pulp chamber
B: In dentin
Answer: B: In dentin 
Explanation: None