What must you be aware of here?

Your answer is correct.

According to German traffic rules:

1. It is not permitted to stop to the left of the boundary line of the carriageway because that area is usually reserved as a hard shoulder or emergency lane, and stopping there would obstruct traffic flow or emergency operations.

2. Slower moving vehicles must use the hard shoulder if possible to allow faster vehicles to pass safely on the carriageway.

However, driving or crossing the boundary line of the carriageway is not prohibited at all times—there are exceptions, such as when entering or leaving the hard shoulder. Therefore, option 3 is incorrect as a general rule.

In summary, the rules ensure that slower vehicles keep to the hard shoulder where possible, and stopping on the carriageway or left of the boundary is not allowed, maintaining road safety and traffic flow.