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
1st evidence of calcification of Primary Mandibular 2nd molar is seen in 
Select and explain. 
A. 14 wk IU, B. 16 wk IU, C. 17 wk IU, D. 18-19 wk IU
D: 18-19 wk IU
Answer: D: 18-19 wk IU 
Explanation: None