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
[{'content': 'What is the advantage of crown down technique: \nSelect and explain. \nA. Zipping is less., B. Working length is less likely to change., C. Better penetration of irrigants., D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Crown-down technique/step back = telescoping technique:\xa0\nCoronal 2/3rd preparation with 15, 20, 25 H file GG drill to flare.\xa0\nApical segment preparation with 10, 15 no. file coronal segment.\xa0\nAdvantages: ZIPPING is less, working length less likely to change, better penetration of irrigant.', 'role': 'assistant'}]