How is it ensured that the rear-view mirror on the bike is working properly?

You answered correctly that the rear-view mirror on a bike must be correctly adjusted and must not be damaged. These are important because a properly adjusted mirror ensures you can clearly see traffic behind you, which is crucial for safe lane changes and awareness. A damaged mirror might distort your view or limit visibility, posing a safety risk. The third option, about not extending beyond the handlebars, is not a legal requirement for the mirror to be considered working properly. The key rules focus on functionality and safety through proper adjustment and undamaged condition.