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
Root completion of the mandibular first molar takes place by the age: 
Select and explain. 
A. 7-8 years, B. 8-9 years, C. 9-10 years, D. 10-11 years
C: 9-10 years
Answer: C: 9-10 years 
Explanation: None