Which component's primary job is to regulate the air entering the engine?

The component responsible for regulating the air entering the engine is the throttle body. It plays a crucial role in controlling the amount of air that flows into the intake manifold and subsequently into the engine's cylinders. The throttle body works in conjunction with the accelerator pedal; when the driver presses the pedal, the throttle opens wider to allow more air in, which is necessary for increased engine power. By adjusting the air intake, the throttle body helps manage the engine's performance and efficiency, ensuring it operates smoothly under various load conditions.

In contrast, while the intake manifold is essential for distributing the air-fuel mixture to the engine cylinders, it does not actively regulate the air flow; rather, it serves more as a delivery system. The exhaust manifold is tasked with directing exhaust gases away from the engine after combustion and does not have a role in air intake regulation. The fuel pump's primary function is to supply fuel to the engine, playing no direct part in the regulation of air entering the engine. Thus, the throttle body is clearly the correct answer when considering the component that controls air intake regulation in an engine.