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 post preparation in distal canal of mandibular first molar, maximum chance of perforation is seen in: 
Select and explain. 
A. Lingual surface, B. Distal surface, C. Buccal surface, D. Mesial surface
D: Mesial surface
Answer: D: Mesial surface 
Explanation: None