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
What must an instrument do to completely clean the canal space? 
Select and explain. 
A. Be deflected at the canal orifice, B. Be 2 to 3 mm short of the radiographic apex, C. Fit loosely into the canal, D. Contact all walls and surfaces
D: Contact all walls and surfaces
Answer: D: Contact all walls and surfaces 
Explanation: None