According to Article 59 of the Road Traffic Safety Law Implementation Regulations, when driving a passenger bus at night on unlit roads, how must the driver signal when approaching sharp curves, slope crests, narrow bridges, or uncontrolled intersections?

1. Alternately switch between high and low beams (远、近光灯交替使用) at least twice to give visual warning to unseen road users
2. Turn off all vehicle lights completely for five seconds
3. Maintain high beams continuously while honking non-stop
4. Activate the right turn signal and accelerate across the crest