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 periodontal ligament is approximately 
Select and explain. 
A. 0.25 mm in thickness, B. 0.5 mm in thickness, C. 0.75 mm in thickness, D. 1.0 mm in thickness
A: 0.25 mm in thickness
Answer: A: 0.25 mm in thickness 
Explanation: None