What happens when the LH/RH ENG FIRE PUSH switchlights are selected?

When the LH/RH ENG FIRE PUSH switchlights are selected, the system initiates a series of critical actions designed to respond to a potential engine fire. This includes closing the fuel, bleed air, and hydraulic shutoff valves for the affected engine. This action is crucial because it helps to prevent any flammable fluids from feeding a fire, effectively isolating the engine from the aircraft's systems.

Additionally, while the primary focus is on shutting off fuel and other systems related to the engine, it’s noteworthy that this action does not shut down all electrical systems; rather, it focuses on those specifically associated with the affected engine. By cutting off the necessary supplies and isolating the engine, the safety of the aircraft and its occupants is maintained during a fire event.

Thus, the correct answer encompasses all these vital systems being shut off, making option D the most comprehensive and accurate choice.