Under road traffic regulations, what actions must a commercial driver take when encountering dense fog with visibility dropping below 50 meters on an expressway?

1. Turn on fog lights, low beams, clearance lights, and hazard warning flashers, reduce speed to below 20 km/h, and exit the expressway at the nearest exit or rest area as soon as possible
2. Turn on high-beam headlights and accelerate to 100 km/h to pass through the fog bank rapidly
3. Stop immediately in the middle lane of the expressway and wait for the fog to clear
4. Follow 2 meters behind another vehicle's taillights