According to Article 81 of the Implementation Regulations of the Road Traffic Safety Law, when driving a passenger bus on an expressway in fog or heavy rain with visibility less than 200 meters (能见度小于200米), what are the speed and following distance rules?

1. Speed must not exceed 80 km/h, and following distance must be at least 50 meters
2. Turn on fog lights, low beams, clearance lamps, and front/rear position lamps; speed must not exceed 60 km/h, and following distance must be at least 100 meters
3. Speed must not exceed 40 km/h, and following distance must be at least 30 meters
4. Turn on high beams and maintain normal cruising speed of 100 km/h