What is the correct response if, when reversing a combination vehicle the view to the rear is impeded?

When reversing a combination vehicle (for example a car with a trailer or a truck with a trailer), your main duty is to make sure you do not endanger anyone. If your direct view to the rear is blocked and you rely on a person directing you, that person effectively becomes your “eyes” for the danger area behind the vehicle.

That’s why answer 1 is correct: if you lose visual contact with the person directing you, you must stop immediately. Without continuous communication/line-of-sight, you can’t be sure the area is still clear, and continuing to reverse would be blind reversing, which is not allowed because it creates an unacceptable risk for pedestrians, cyclists, obstacles, or sudden changes in the situation.

A good rule of thumb for similar questions: reversing is only permitted when you can supervise the rear area at all times. If you can’t do that yourself, you need reliable guidance, and the moment that guidance is no longer reliably available, you stop and only continue once the situation is clear again.