According to Article 52 of the PRC Road Traffic Safety Law Implementation Regulations, at what minimum distance behind a disabled heavy truck must the reflective warning triangle (警告标志) be placed on an expressway?

1. At least 150 meters behind the vehicle (and at least 200 meters at night or in adverse weather)
2. 50 meters behind the vehicle under all conditions
3. 10 meters directly next to the rear bumper
4. On top of the truck roof cab spoiler