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
Retention form of endodontics is: 
Select and explain. 
A. Creation of an apical stop to prevent extrusion of material of beyond apex., B. Creation of nearly parallel walls in apical 3rd to give tug back to master cone., C. Access should be expanded so that the instrument do not bind., D. None of the above
B: Creation of nearly parallel walls in apical 3rd to give tug back to master cone.
Answer: B: Creation of nearly parallel walls in apical 3rd to give tug back to master cone. 
Explanation: None