Final answer:
The safest speed to reverse a vehicle from the given multiple-choice options, especially in conditions with poor visibility, is 10 km/h. This speed allows for better control and safer maneuvering.
Step-by-step explanation:
When driving a vehicle in reverse, it's important to ensure safety by moving at a slow, controlled speed. Generally, there is no universal speed set for reversing, but the question presents a multiple-choice option. The safest speed from the choices given, notably in conditions where visibility is not good, is 10 km/h. This speed allows the driver to have better control over the vehicle and to react to any unexpected obstacles. Exceeding this speed while reversing—especially in poor visibility—increases the risk of an accident.
It's important to note that the speed at which a vehicle can safely reverse may depend on various factors including the type of vehicle, the environment, and the driver's proficiency. Always follow local traffic regulations and guidance from driving authorities when operating a vehicle.