In a typical oil-fired heating system, which one of the following is the direct purpose served by the cadmium sulfide cell (commonly called the CAD cel?
a. The CAD cell delivers electricity to the electrodes that provide the spark.
b. The CAD cell is part of the thermostat mounted in the room to control the temperature.
c. The CAD cell is a safety device that monitors the burner flame.
d. The CAD cell is the fuel nozzle that's used to distribute the fuel in the burner.