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
The time taken for primary tooth root completion after eruption: 
Select and explain. 
A. 3 years, B. 1 year, C. 2 years, D. 1 month
B: 1 year
Answer: B: 1 year 
Explanation: None