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
What fraction of life do we spend chewing with primary teeth 
Select and explain. 
A. 5%, B. 6%, C. 7%, D. 8%
B: 6%
Answer: B: 6% 
Explanation: Considering average age which a human being lives as 70 years, only 6% of our life span uses primary teeth.