You are presented with the question "What is used as an energy source by pagers?" and the following answer choices: 
- Wi-Fi
 - photons
 - antennae
 - energy
 - Heart rate
 - fire
 - layers of fat
 - electricity

Now knowing that electricity is used as an energy source by electrical devices and devices such as pagers and cell phones are forbidden, choose the best answer.


 

        electricity 