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
Which of the following is the common factor for the initiation of both dental caries and periodontal disease 
Select and explain. 
A. bacterial plaque, B. lactic acid, C. calculus, D. no common factor
A: bacterial plaque
Answer: A: bacterial plaque 
Explanation: None