Fact 1: Burning wood is used to produce heat.

Fact 2: Birch trees are deciduous and the wood burns hot and fast, as if soaked with oil or kerosene.

Given the two facts above, answer the question "Birch trees are wood that are used to produce what?" with the following options: 
- sweets
 - ice
 - water
 - energy
 - heat
 - food
 - sugar
 - paper


 

     heat    