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
Which of the following best describes the resistance form in endodontic root canal preparation? 
Select and explain. 
A. The establishment of apical tug back resistance to prevent the apical root fracture during obturation, B. The cavity form which is obtained for application of condenser in vertical compaction, C. The cavity form which is designed for application of condenser in lateral compaction, D. Cavity form which is designed to obtain for entry of condenser during obturation
A: The establishment of apical tug back resistance to prevent the apical root fracture during obturation
Answer: A: The establishment of apical tug back resistance to prevent the apical root fracture during obturation 
Explanation: None