A technician is called to assist a customer. The customer reports when they powered on the system, they heard a loud noise, saw a spark, and smelled a burning smell. Which of the following should the technician advise the customer to do FIRST?
A. Power on the system, to see if it happens again.
B. Immediately notify the fire department.
C. Unplug the system from the power source.
D. Turn off the circuit breaker to the building.