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
Calcification of roots of deciduous teeth is completed by: 
Select and explain. 
A. 2 years, B. 4 years, C. 6 years, D. 8 years
B: 4 years
Answer: B: 4 years 
Explanation: None