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
During root canal preparation for post, what should be the length of remaining apical GP seal? 
Select and explain. 
A. 3 mm, B. 4 mm, C. 5 mm, D. 6 mm
C: 5 mm
Answer: C: 5 mm 
Explanation: None