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
Pulp of involved teeth is vital in the following 
Select and explain. 
A. Apical cyst, B. Granuloma, C. Apical periodontitis, D. Phoenix abscess
C: Apical periodontitis
Answer: C: Apical periodontitis 
Explanation: None