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
Inflammation of the perapical tissue is sustained by which of the following 
Select and explain. 
A. Stagnant tissue fluid, B. Necrotic tissue, C. Microorganisms, D. Pus cells
C: Microorganisms
Answer: C: Microorganisms 
Explanation: None