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
Senile caries refers to: 
Select and explain. 
A. Residual caries., B. Root caries., C. Pit and fissure caries, D. Recurrent caries.
B: Root caries.
Answer: B: Root caries. 
Explanation: Root caries or senile caries occur on the tooth that has been exposed to the oral environment.