Final answer:
The narrator pressed down on the accelerator to increase the car's speed, which is consistent with the principle of acceleration, involving the increase in velocity of the vehicle.
Step-by-step explanation:
The narrator pressed down on the accelerator to increase speed. Pressing down on the accelerator in a car causes an increase in the flow of gasoline to the engine, which in turn increases the car's velocity. This action relates to the principle of acceleration, which is defined as a change in velocity, whether in speed, direction, or both. In this context, the narrator's intention was to increase the speed of the vehicle, making d. The narrator pressed down on the accelerator to increase speed the correct answer. This is because acceleration in a vehicular sense typically refers to increasing the magnitude of velocity, which means going faster.