Fact 1: Burning wood is used to produce heat.

Fact 2: Heating and air conditioning keep the building comfortable regardless of the temperature outside.

Given the two facts above, answer the question "burning wood is used to keep buildings what?" with the following options: 
- comfortable
 - closed
 - homogenous
 - warmth
 - smokey
 - cold
 - staying warm
 - freezing


 

 comfortable        