Fact 1: The number of rings in a tree trunk can be used to estimate the age of the tree.

Fact 2: Age of Pine trees (AGE) in years.

Given the two facts above, answer the question "what unit of time can be estimated by the rings in a tree trunk?" with the following options: 
- hours
 - decades
 - months
 - H20
 - Joules
 - DNA
 - years
 - seasons


 

       years  