Can a passenger car transport a load on the roof rack?

A)Yes, but only when travelling during the day.
B)No.
C)Yes, when it does not compromise the stability of the vehicle.Correct
The load carried in a vehicle, as well as the accessories used for its securing or protection, must be arranged and, if necessary, fastened in such a way that they cannot compromise the stability of the vehicle.
Placing objects on the roof rack will increase aerodynamic drag and therefore fuel consumption, so whenever possible we should place things in the boot.
Placing objects on the roof rack will increase aerodynamic drag and therefore fuel consumption, so whenever possible we should place things in the boot.