When driving with high beams (feux de route) on an unlit road at night, when MUST a driver switch to low beams (feux de croisement)?

1. When about to cross an oncoming vehicle or when closely following another vehicle
2. Only when entering a national park or wildlife reserve
3. Only if the oncoming driver flashes their high beams first
4. High beams must never be switched off on unlit rural highways