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
Most important step in root canal preparation? 
Select and explain. 
A. Biomechanical preparation, B. Obturation, C. Access canal opening, D. None of the above
A: Biomechanical preparation
Answer: A: Biomechanical preparation 
Explanation: None