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 initiative factor for periodontitis is: 
Select and explain. 
A. Dental plaque, B. Calculus, C. Trauma from occlusion, D. Food debris layer
A: Dental plaque
Answer: A: Dental plaque 
Explanation: None