Which items are part of the fuel system in a commercial vehicle?

The fuel system in a commercial vehicle is responsible for storing, transporting, and providing fuel to the engine. The identified components of the fuel system include both the crossover line and the fuel tank.

The fuel tank serves as the primary storage unit for fuel; it holds gasoline or diesel that supplies the engine. The crossover line, typically present in vehicles with multiple fuel tanks, allows fuel to flow between tanks, ensuring that the vehicle has a consistent and adequate fuel supply. These two components work together to ensure that fuel is delivered efficiently and effectively to the engine, which is vital for vehicle operation.

In contrast, the other options mention components that do not belong to the fuel system. The fuel filter, mentioned in one option, is indeed a vital part of the fuel system, but it is paired incorrectly with an air line, which is related to the vehicle's air system, not the fuel system. Similarly, the oil filter and coolant reservoir deal with the engine's lubrication and cooling systems, and the exhaust manifold and muffler pertain to the exhaust system. Therefore, option A is the correct choice as it specifically includes components that are integral to the fuel system of a commercial vehicle.