Fact 1: Aswitch is used to start the flow of current in an electrical circuit.

Fact 2: Some systems have an additional connection for a second doorbell switch.

Given the two facts above, answer the question "What is used to start the flow of current in an electrical circuit?" with the following options: 
- energy
 - a doorbell
 - heat energy
 - kinetic energy
 - simple
 - Firecrackers
 - cycles
 - deltas


 

  a doorbell       