What is the general lane discipline rule (Rechtsfahrgebot) under StVO § 7 for a tractor driving along an open multi-lane road outside built-up areas?

1. Drive in the middle of the carriageway so that following vehicles cannot pass at an unsafe point
2. Use whichever lane keeps the implement clear of the kerb, including the left-hand lane
3. Drive as far to the right as is safe and reasonable, keeping to the rightmost lane
4. Change lanes regularly so that following drivers are not held up behind the same vehicle