Which of the following driving maneuvers is strictly prohibited inside road and expressway tunnels under Chinese traffic regulations?

1. Overtaking other vehicles, changing lanes across solid white lines, making U-turns, reversing, or parking arbitrarily
2. Maintaining a steady speed within the posted tunnel speed limit
3. Keeping a safe following distance of at least 100 meters from the vehicle ahead
4. Operating low-beam headlights throughout the tunnel