Aswitch is used to start the flow of current in an electrical circuit, and some systems have an additional connection for a second doorbell switch. Given these facts, what is used to start the flow of current in an electrical circuit among the following options:
- energy
 - a doorbell
 - heat energy
 - kinetic energy
 - simple
 - Firecrackers
 - cycles
 - deltas


 

  a doorbell       