Fact 1: Some light bulbs convert electricity into light and heat energy.

Fact 2: Conventional light bulbs generate light by heating a filament.

Given the two facts above, answer the question "What type of energy do filaments use to illuminate?" with the following options: 
- energy
 - nektar
 - fibers
 - cacti
 - burn
 - copper
 - Heat
 - two


 

       Heat  