What is the primary structure of a body on frame construction?

The primary structure of a body on frame construction consists of a separate body mounted on a rigid chassis. This design involves a robust framework that supports the vehicle's components, including the engine, transmission, and suspension. The body is not integrated with the chassis, which allows for better flexibility in design and modifications. This construction method is commonly used in trucks and SUVs because it provides enhanced durability and the capability to absorb impacts, making it suitable for heavy-duty applications.

The separate nature of the body and chassis also allows for easier repairs and replacements, as damaged parts can be exchanged without having to replace the entire vehicle structure. Additionally, this design can accommodate larger body designs, which is important in the truck segment where cargo capacity and passenger space are crucial. The other options, while interesting concepts, do not accurately represent the primary characteristic of body on frame construction.