According to Article 52 of the PRC Road Traffic Safety Law, at what distance behind a disabled vehicle must a warning sign (warning triangle / 警告标志) be placed on regular urban or rural roads?

1. 1 to 2 meters directly against the rear tire
2. 50 to 100 meters behind the vehicle in the direction of oncoming traffic
3. 500 to 1000 meters behind the vehicle
4. Warning signs are not required on regular roads