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

Fact 2: Tree rings are examined to learn the forest age and growth rate.

Given the two facts above, answer the question "What can be used to estimate a forest's growth rate?" with the following options: 
- rings
 - fibers
 - bamboo
 - bark
 - crown
 - wind
 - soil
 - traits


 

 rings        