Which construction method uses body parts welded together to form an integral frame?

The correct answer is unibody. This construction method is characterized by the body parts being welded together, creating a single cohesive structure rather than relying on a separate frame. In a unibody vehicle, the body and the frame are integrated into one continuous piece, which enhances structural integrity, reduces weight, and typically provides better safety performance in collisions. The all-in-one design allows for improved handling and fuel efficiency, making the unibody method a preferred choice in modern automotive design.

While the other options represent different vehicle construction methods, they do not feature the same welded integration as unibody construction. For example, the body-on-frame method involves a distinct frame that supports the body as a separate component. Monocoque refers to a design where the outer skin provides strength, but it isn't specifically tied to the welding process as unibody construction is. Composite construction involves the use of multiple materials but does not specifically refer to a welded body structure either. Therefore, unibody is the clearly defined choice in this context.