Under MOT regulations, when MUST a road passenger transport enterprise assign at least TWO qualified commercial drivers (配备2名以上驾驶员) to a single vehicle?

1. Only when the coach carries foreign tourists
2. Whenever the ambient outside temperature exceeds 35°C
3. Only during national public holidays
4. When the single-trip operating distance exceeds 400 km (or exceeds 600 km on expressways) or operating duration exceeds 8 hours