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
Obturation of a root canal should achieve 
Select and explain. 
A. Tug-back, B. hermetic seal, C. Fluid-free seal, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None