Final answer:
The driver of the vehicle is mainly responsible for ensuring loads are balanced and secured. A bouncing trailer on a highway is likely nearly empty because weight would otherwise keep it stable.
Step-by-step explanation:
The responsibility for ensuring that loads are balanced and secured at all times falls primarily on d. The driver of the vehicle. While the owner of the cargo and the vehicle manufacturer may play roles in ensuring the safety and security of the load before the trip, it is ultimately the driver's responsibility to make sure that these standards are maintained throughout the transport. When observing a freight truck's trailer bouncing up and down slowly on the highway, it is more likely that the trailer is nearly empty. A heavily loaded trailer would have less bounce due to the weight keeping it stable on the road. The oscillation observed in an empty trailer is due to the lack of weight, which allows the suspension to move more freely.