Which vehicles must always be marked by their own lights or parking warning plates when parked on the roadway at dusk or in darkness in built-up areas?

You answered correctly. In built-up areas at dusk or in darkness, both trucks and motor caravans with a permissible total mass over 3.5 tons, as well as trailers, must always be marked by their own lights or parking warning plates when parked on the roadway. This rule increases visibility to prevent accidents, as these larger vehicles present a greater obstacle for other road users. Ordinary cars do not require additional marking in these conditions within built-up areas if street lighting is sufficient. Always remember that larger and less visible vehicles need special marking for safety at night or in poor visibility.