What is the advantage of crown down technique:: (A) Zipping is less., (B) Working length is less likely to change., (C) Better penetration of irrigants., (D) All of the above.
Answer is D. 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.