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
[{'content': 'Ligamentum denticulatum is: \nSelect and explain. \nA. Only a pair of pial extension, B. A dural derivative, C. Arachnoid extension only, D. Extends to sacral segments only', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]