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
According to Schilder mechanical objectives of cleaning and shaping are: 
Select and explain. 
A. Canal should be continuously taper., B. Canal should be prepared in multiple plane., C. Apical construction should be as small as possible., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: Mechanical objectives by (SCHILDER)
i) Canal should be continuously taper Funnel orifice →Apex.
ii) Canal should be prepared in multiple plane.
iii) Apical constriction should be as small as possible.