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
First appearance of tooth formation occurs in: 
Select and explain. 
A. 6th week IU, B. 2nd week IU, C. 9th week IU, D. 4th month IU
A: 6th week IU
Answer: A: 6th week IU 
Explanation: None