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
2nd optimal landmark for termination of cleaning, shaping and obturation is 
Select and explain. 
A. Apical constriction, B. Cementodentinal junction, C. Major diameter, D. None of the above
A: Apical constriction
Answer: A: Apical constriction 
Explanation: None