You are presented with the question "Trees have woody stems covered with what?" and the following answer choices: 
- heat energy
 - thin skin
 - protective skin
 - skinny cells
 - white skin
 - Chlorophyll
 - Organic compounds
 - looseness

Now knowing that trees have woody stems covered with bark and on the outside is a protective skin of bark made mainly of cork, choose the best answer.


 

   protective skin      