When is it forbidden to tow a motor vehicle with a rigid coupling?

Explanation

Even with a rigid coupling, the driver of the towed vehicle must be able to steer it. If the steering mechanism is faulty, the vehicle cannot be controlled, so towing it is forbidden. In that case it must be carried loaded onto a recovery vehicle’s platform. The other options are wrong because they are not about the vehicle’s controllability. For example, an icy road limits towing with a flexible coupling but does not forbid towing with a rigid one. Faulty hazard warning lights are not a reason to forbid towing if the vehicle’s visibility is ensured by other means. Darkness on its own does not forbid towing either, as long as the lighting and visibility requirements are met.