Fact 1: Agreenhouse is used to protect plants from the cold.

Fact 2: Agreenhouse is made entirely of glass.

Given the two facts above, answer the question "What can be used to protect plants from the cold?" with the following options: 
- ice
 - fibers
 - metal
 - peat
 - keratin
 - oil
 - glass
 - snow


 

       glass  