Fact 1: Trees have woody stems covered with bark.

Fact 2: Bark on mature trees runs 6 to 12 inches thick, insulating the tree against fire damage.

Given the two facts above, answer the question "What do trees have that insulates?" with the following options: 
- hats
 - looseness
 - dogs
 - woody stems
 - food and shelter
 - cells
 - storing water
 - In their leaves


 

    woody stems     