What is a key part of a steering system?

The steering wheel serves as the primary interface through which the driver controls the direction of the vehicle. When the driver turns the steering wheel, it initiates a series of mechanical actions that result in the turning of the vehicle's wheels, directing its path. This component is essential for maneuvering the vehicle safely and effectively, allowing for quick adjustments in direction as needed.

In the context of the other options, while brake pads are crucial for slowing or stopping the vehicle, transmission fluid is necessary for the operation of the vehicle's transmission, and a fuel filter helps maintain the engine's performance by removing impurities from fuel, none of these items play a direct role in the steering mechanism of the vehicle. Therefore, the steering wheel is the key element of the steering system, making it critical for vehicle control.