Which of the following is a risk factor that could affect a vehicle's center of gravity?

Improper tire inflation is a risk factor that can affect a vehicle's center of gravity because it alters the vehicle's handling and balance. When tires are not inflated to the manufacturer's recommended pressure, it can change the height of the vehicle, particularly if the tires are significantly under-inflated or over-inflated. This can impact the overall stability of the vehicle, especially during turns or sudden maneuvers.

In contrast, using premium grade gasoline does not influence the physical structure or balance of the vehicle but may offer better performance in terms of engine efficiency. Driving at night primarily affects visibility rather than the vehicle's mechanics or center of gravity. Having a full tank of gas does alter the weight distribution, but it does not impact the center of gravity in the same way that improper tire inflation can, as it is a consistent factor that should be considered when assessing the vehicle's operational weight.