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
Ramjford index is used on: 
Select and explain. 
A. All permanent teeth, B. Selected six permanent teeth, C. Selected twelve permanent teeth, D. None of the above
B: Selected six permanent teeth
Answer: B: Selected six permanent teeth 
Explanation: None