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
Thumb sucking is normal during: 
Select and explain. 
A. The first year of life., B. First 2 years of life., C. First 3 years of life., D. First 4 years of life.
B: First 2 years of life.
Answer: B: First 2 years of life. 
Explanation: None