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
Eruption of Mandibular 1st molar occur at 
Select and explain. 
A. 8 years, B. 7 years, C. 9 years, D. 6 years
D: 6 years
Answer: D: 6 years 
Explanation: None