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 period of infancy usually refers to: 
Select and explain. 
A. First 2 years after birth, B. First 1 year after birth, C. First 6 months after birth, D. First 3 years after birth
B: First 1 year after birth
Answer: B: First 1 year after birth 
Explanation: None