What is included in the exterior panels of a vehicle?

The exterior panels of a vehicle encompass components that form the outer surface and contribute to the vehicle's shape, aesthetics, and structural integrity. The hood assembly, which is the correct answer, is a critical part of this exterior structure. It serves both functional and protective roles, covering the engine compartment and facilitating access for maintenance and inspections. The hood is also essential for the overall design and aerodynamics of the vehicle.

In contrast, the other options do not belong to the category of exterior panels. The exhaust system is an integral mechanical component that is typically located underneath the vehicle. The transmission casing is part of the drivetrain, housed within the vehicle's undercarriage, and is responsible for housing the transmission, which is not visible from the exterior. The underbody frame supports the entire vehicle structure but does not contribute to the exterior appearance. Thus, the hood assembly is the only option that accurately represents a part of the vehicle's exterior panels.