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: Pathology
Focal sclerosing osteomyelitis is: 
Select and explain. 
A. Due to excessive periosteal bone formation, B. An extremely painful condition, C. Due to low grade chronic infection, D. A common sequel following sequestrectomy
C: Due to low grade chronic infection
Answer: C: Due to low grade chronic infection 
Explanation: None