For which vehicles in commercial goods traffic do you need a permit?

You answered correctly. In commercial goods transport in Germany, a permit is required for vehicles with a permissible total mass of 3.5 tons or more. This includes both the vehicle itself and any trailers. In this question, vehicles with a total mass of 8 t including trailers (answer 1) and 4 t excluding trailers (answer 2) both exceed this threshold, so a permit is required for each. Vehicles with a total mass of only 3 t including trailers (answer 3) do not require a permit, as they are under the 3.5-ton rule. Always check the total permissible mass and whether trailers are counted to determine permit requirements in commercial goods traffic.