Final answer:
The described action is Engine shutdown with accessory mode, which saves fuel by turning off the car's engine while allowing electrical accessories to remain on, powered by the battery.
Step-by-step explanation:
The action that best describes what the student's wife is doing when she turns off the car engine but keeps the AC and other electrical accessories on is C) Engine shutdown with accessory mode. This means that the vehicle's engine is turned off to save fuel, but the electrical accessories, such as the air conditioning, can continue to operate using the car's battery power.
This is different from engine idling, which involves keeping the engine running at a low speed, not turning it off. It’s also distinct from a hybrid driving mode, which refers to a hybrid car that can switch between gasoline and electric propulsion. Electric vehicle conservation mode is not applicable because it pertains to fully electric vehicles, and here we're discussing an internal combustion engine shutting down while accessories remain powered.