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
What type of fibers are principal fibers of the PDL? 
Select and explain. 
A. Elastic, B. Reticular, C. Collagenous, D. Collagenous and elastic
C: Collagenous
Answer: C: Collagenous 
Explanation: None