Final answer:
Never pass closely behind a truck preparing to back up or slowing down, and a trailer that bounces up and down slowly is likely nearly empty because the lack of weight causes more bounce.
Step-by-step explanation:
Never pass close behind a truck that is preparing to back up or is in the process of slowing down. Most trailers are eight feet wide and completely hide objects behind them. As for the inquiry about the trailer's bouncing movement, it is more likely that the trailer is nearly empty. A heavily loaded trailer would have less bounce because the weight stabilizes it. However, when a trailer is nearly empty, it lacks the mass to dampen the road's irregularities; thus, it bounces more.