Before you can have in-car entertainment, you had to have the internal combustion engine. =D

The accelerator more or less synonymous with throttle. Throttle governs the amount of air, and by a function of that fuel that is let into the engine. Yung revs etc. etc. are just a by-product of this.

Case A is more or less correct, pero instead of the amount of air being a function of the fuel you let in, it's the reverse. The amount of fuel is a function of the amount of air you let into the engine. Conversely, C is also correct. Since the accelerator governs the throttle, stepping off the accelerator also closes the throttle, meaning you stop/limit air, and therefore fuel from entering the engine.

Before the days of electronic fuel-injection, the amount of fuel is more or less linearly related to the amount of air, both being fed into the carbuerator. Because of this linear relationship, old carb cars are often run rich for safety, kaya pag dating sa high-altitude environment (i.e. baguio) minsan nalulunod sa gas.

These days, the amount of fuel needed is calculated by the ECU, by sensing the amount of air coming into the engine via a MAF (mass airflow sensor) or MAP (mass air pressure sensor).

Yun lang po! Basta to summarize: at the very basic level, the accelerator controls the amount of AIR coming into the engine, tapos yung ECU or carb mo na ang bahala sa amount of fuel. More air = more power = more revs. Lahat na ng succeeding driving characteristics ng engine madederive mo dito.