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
In CPITN index zero score means: 
Select and explain. 
A. Gingival bleeding, B. Grade 1 mobility of teeth, C. Healthy tooth, D. Spontaneous bleeding
C: Healthy tooth
Answer: C: Healthy tooth 
Explanation: None