Fact 1: Atelephone is used for communication by humans over long distances.

Fact 2: Telephone lines conduct electricity.

Given the two facts above, answer the question "What is used for communication by humans over long distances?" with the following options: 
- A Greek letter
 - electricity
 - airplanes
 - kinetic energy
 - trains
 - sign language
 - photons
 - messengers


 

  electricity       