You want to pull a trailer. When do additional rear-view mirrors have be to attached to your motor vehicle?

You are correct in selecting answer 1. According to German traffic rules, you must attach additional rear-view mirrors to your vehicle when you are unable to see all important road situations with the standard mirrors alone. The law requires that you always have a complete view of the traffic behind and to the side of your vehicle and trailer. It's not about the type or size of the trailer specifically; it’s about whether your rearward visibility is adequate. If the trailer blocks your view with the existing mirrors, extra mirrors are required to ensure safety. Always check your rear view before driving with a trailer, and use additional mirrors if needed.