A Vacuum-Assist Brake Booster works using ______.

A Vacuum-Assist Brake Booster functions primarily by utilizing manifold vacuum in conjunction with atmospheric pressure to enhance the braking force applied by the driver.

The manifold vacuum is created in the engine's intake manifold when the engine runs, and it serves as the key fuel for creating the necessary pressure differential that activates the brake booster. When the driver presses the brake pedal, the brake booster uses this manifold vacuum to amplify the force exerted on the brake master cylinder, thereby improving braking efficiency and responsiveness.

Atmospheric pressure plays a role in this process as well, acting in contrast to the vacuum created in the manifold. The disparity between the two pressures assists in the operation of the booster, allowing for greater force multiplication with minimal effort from the driver.

The inclusion of "atmospheric vacuum" in the other choices adds confusion because "atmospheric vacuum" is not a standard term used in this context. Atmospheric pressure is relevant, but it doesn't imply a vacuum state. Thus, the combination of manifold vacuum and atmospheric pressure accurately describes the operation of a Vacuum-Assist Brake Booster without ambiguity, making this choice the most fitting among the presented options.