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': 'Obturation of a root canal should achieve \nSelect and explain. \nA. Tug-back, B. hermetic seal, C. Fluid-free seal, D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]