Why should you allow the truck to change lane?

You answered correctly with options 1 and 2, which are the right reasons to allow a truck to change lanes.

According to German traffic rules, you should give way to a truck changing lanes because the truck driver might have limited visibility and may not see your vehicle clearly. This is important for safety, as trucks have larger blind spots. Additionally, showing due consideration to the truck driver helps prevent accidents and ensures smooth traffic flow.

Option 3, "Because the alternate merging procedure applies here," is not correct in this context. The alternate merging procedure (Wechselverkehrsverfahren) is a special rule that applies in certain situations like lane closures, but it does not automatically require you to allow a truck to change lanes in all cases.

In summary, always be aware of trucks' limited visibility and show consideration by adjusting your speed or position to facilitate their safe lane change. This is a key part of cooperative and safe driving in Germany.