Fact 1: Aflashlight requires a source of electricity to produce light.

Fact 2: Flashlights provide the safest emergency lighting source.

Given the two facts above, answer the question "What requires a source of electricity to produce light?" with the following options: 
- Broken light bulb.
 - The sun.
 - basic building blocks of life
 - an electron microscope
 - The source magazine.
 - algae and plants
 - the simplest of green plants
 - An emergency lighting source.


 

        An emergency lighting source. 