Final answer:
The statement that engines of placarded vehicles must be shut off when fueling is true for safety reasons. This prevents potential ignition sources during fueling. Moreover, fuel consumption in gasoline engines and energy management in other systems like cooking or solar cells operate under different principles.
Step-by-step explanation:
The statement The engine of a placarded vehicle must be shut off when fueling is true. This is a safety regulation that is intended to prevent accidents due to fire or explosions. When fueling, the engine could serve as a source of ignition due to the high temperatures or sparks it can produce. Furthermore, when it comes to energy management, a gasoline engine optimizes fuel consumption at lower speeds, and in contrast to solar cells, which capture sunlight to generate electricity, gasoline engines depend on the combustion of fuel to generate energy. During this process, more energy is added to the engine, which is a stark contrast to how energy is handled during cooking, where the energy given to the system remains constant throughout the process.