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
There is a real relationship between the incidences of fracture of anterior teeth and the 
Select and explain. 
A. caries in those teeth, B. hardness of the enamel, C. hardness of dentin, D. protrusion of those teeth
D: protrusion of those teeth
Answer: D: protrusion of those teeth 
Explanation: None