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
Russel's periodontal index scores range from 
Select and explain. 
A. 0-2, B. 0-4, C. 0-6, D. 0-8
D: 0-8
Answer: D: 0-8 
Explanation: None