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
The most abundant principal fibre group in periodontal ligament is: 
Select and explain. 
A. Horizontal, B. Transeptal, C. Apical, D. Oblique
D: Oblique
Answer: D: Oblique 
Explanation: None