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
The purposes of cavity preparation is/are: 
Select and explain. 
A. Removal of all the defects of enamel, dentin  and cementum, B. To  locate the  margins  of restoration as  conservatively  as  possible, C. To allow for  esthetic and functional placement of restorative  material, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Cavity design should be in biologic and structural harmony with tooth tissues.