C

Nice, very fun puzzle! I may be nitpicking, but SPARKPLUGs aren’t technically really a “device to start an engine.” They fire continuously as an engine runs to trigger combustion, but the device that actually starts most modern engines is a starter motor initiated by the battery. Spark plugs are involved, sure… but only as much as any other component of the engine necessary to keep it running, such as a carburetor, fuel pump, etc.