Fact 1: Trees have woody stems covered with bark.

Fact 2: During the stripping, the protective layer of inner bark is removed.

Given the two facts above, answer the question "Trees have woody stems covered with what?" with the following options: 
- food and shelter
 - smooth ridges
 - looseness
 - protective layer
 - Organic compounds
 - plastic sheet
 - heat energy
 - thin metal


 

    protective layer     