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
Prepubertal periodontitis occurs 
Select and explain. 
A. Before 11 yrs, B. At 12-15 years, C. At 18 years of age, D. After 20 years
A: Before 11 yrs
Answer: A: Before 11 yrs 
Explanation: None