At night, how must you secure a vehicle which has broken down at a place where it constitutes a danger to other traffic?

You answered correctly by selecting to immediately switch on the hazard warning lights and to place a warning triangle at a sufficient distance. These measures are required because they make your vehicle more visible to other road users in the dark and warn approaching traffic about the danger. Hazard warning lights alert others right away, and the warning triangle gives advance notice from a distance. Switching on the reversing lights is not appropriate in this situation, as reversing lights are only used to indicate the vehicle is moving backwards and could mislead other drivers. For similar situations at night or in low visibility, always use hazard warning lights and a warning triangle to secure your vehicle and ensure safety for everyone on the road.