According to Article 43 of the PRC Road Traffic Safety Law, under which of the following mountain road conditions is overtaking (超车) strictly prohibited?

1. When traversing sharp curves, narrow bridges, steep crests, tunnels, or sections where oncoming traffic is present
2. On straight sections of two-lane national highways with broken yellow centerlines
3. When the vehicle ahead is an agricultural tractor moving at 10 km/h on a clear wide straightaway
4. When following a vehicle traveling below the posted minimum speed on an open multi-lane expressway