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
Common sign of occlusal trauma (TFO) is 
Select and explain. 
A. Tooth mobility, B. Fractures of cusps, C. Resorption of alveolar ridge, D. Widening of P.D ligament
A: Tooth mobility
Answer: A: Tooth mobility 
Explanation: None