Which components are found on a trailer equipped with spring parking brakes?

The correct choice identifies the key components associated with a trailer that utilizes spring parking brakes. Spring parking brakes are an important safety feature in commercial vehicles, including trailers, which engage automatically when air pressure drops below a certain threshold.

The front service reservoir and rear service reservoir store compressed air needed for the brake system operations. The relay valve serves as the control element that directs air to the appropriate braking chambers. Spring brake chambers are integral to the operation of the spring parking brakes, as they house the springs that apply the brakes when air pressure is released. Together, these components ensure that the trailer can be securely parked and safely controlled.

In contrast, other options mention components that either do not directly relate to the spring parking brake system or pertain to other braking systems altogether. For example, air compressors are crucial for generating compressed air but are more aligned with the overall air system rather than the specific components of spring parking brakes, while items like brake drums and wheel cylinders pertain to drum brake systems rather than the parking mechanism specifically.