Under sign 3.20 'No Overtaking' (red circle with black car on right and red car on left), which of the following may a driver legally overtake?

1. Any passenger car that happens to be travelling below 50 km/h.
2. Slow-moving vehicles, animal-drawn carts, two-wheeled motorcycles without a sidecar, mopeds and bicycles.
3. Buses carrying passengers, when they are in the right-hand lane.
4. Heavy trucks over 12 tonnes on uphill stretches.