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 is the advantage of crown down technique: 
Select and explain. 
A. Zipping is less., B. Working length is less likely to change., C. Better penetration of irrigants., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: Crown-down technique/step back = telescoping technique: 
Coronal 2/3rd preparation with 15, 20, 25 H file GG drill to flare. 
Apical segment preparation with 10, 15 no. file coronal segment. 
Advantages: ZIPPING is less, working length less likely to change, better penetration of irrigant.