Fact 1: Agreenhouse is used to protect plants by keeping them warm.

Fact 2: Retains heat in cold weather, reflects exterior heat in warm weather.

Given the two facts above, answer the question "a greenhouse is used to protect plants by doing what?" with the following options: 
- reduced heat
 - colder and wetter
 - storing lawnmowers
 - holding plant pots
 - retaining heat
 - In the winter
 - food and shelter
 - starting fires


 

     retaining heat    