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
All of the following may result in under filling of a root canal EXCEPT 
Select and explain. 
A. Apical perforation, B. Edge formation, C. Short length estimation, D. Lateral perforation
A: Apical perforation
Answer: A: Apical perforation 
Explanation: None