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
Percussion is a dental diagnostic procedure used in determining whether 
Select and explain. 
A. The tooth is vital, B. The pulp is hyperemic, C. A periodontitis exists, D. All of the above
C: A periodontitis exists
Answer: C: A periodontitis exists 
Explanation: None