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
When assessing tooth mobility the best indicator is 
Select and explain. 
A. Condition of gingival periodontal fibers, B. Horizontal crown displacement, C. Root displacement within the remaining periodontal ligament, D. Amount of calculus and plaque present
C: Root displacement within the remaining periodontal ligament
Answer: C: Root displacement within the remaining periodontal ligament 
Explanation: None