Fact 1: Powering an electrical device with a battery requires a path for electricity to flow through a closed circuit.

Fact 2: Today's cellular phones are second-generation devices.

Given the two facts above, answer the question "Powering what with a battery requires a path for electricity to flow?" with the following options: 
- closed
 - energy
 - complete
 - vehicles
 - engines
 - a phone
 - buses
 - Cars


 

      a phone   