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 is true about master apical file? 
Select and explain. 
A. The last file which is selected for the obturation, B. The initial file which is selected for initial radiographic working length, C. The smaller file used in between the other file during biomechanical preparation, D. The last file which is used for removal of soft debris from root canal
A: The last file which is selected for the obturation
Answer: A: The last file which is selected for the obturation 
Explanation: None