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
What should be ideal depth of MTA for root end filling material? 
Select and explain. 
A. 1 mm, B. 3 mm, C. 5 mm, D. 7 mm
B: 3 mm
Answer: B: 3 mm 
Explanation: None