Final answer:
Compared to a straight truck or bus, a combination vehicle has more items to inspect. A bouncing trailer is more likely to be nearly empty due to a higher response to road bumps.
Step-by-step explanation:
Compared to a straight truck or bus, there are more things to inspect in a combination vehicle. In the scenario provided, if you notice that a freight truck's trailer is bouncing up and down slowly on a highway, it is more likely that the trailer is nearly empty. An empty trailer has less mass and is less likely to be firmly planted on the road, leading to more pronounced and slower bounces as the suspension reacts to uneven road surfaces.