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: Anatomy
Ligamentum denticulatum is: 
Select and explain. 
A. Only a pair of pial extension, B. A dural derivative, C. Arachnoid extension only, D. Extends to sacral segments only
A: Only a pair of pial extension
Answer: A: Only a pair of pial extension 
Explanation: None