Is it permitted to transport people in the back of a truck when towing on a rigid or flexible coupling?

Explication

The official exam accepts the wording “Only permitted in the body of the towing vehicle”; the textually equivalent wording “Allowed only in the body of the towing vehicle” states the same meaning, so the keyed distinction is not unique. The underlying rule permits people in the body of the towing truck but not in the body of the towed truck.