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
In step back technique, the file used for measuring working length is 25 no and it is the first file to be used for Phase 2 i.e. step back technique, the file used for recapitulation will be 
Select and explain. 
A. No 10, B. No 15, C. No 20, D. No 25
D: No 25
Answer: D: No 25 
Explanation: None