Under national standard Electric Vehicles Traction Battery Safety Requirements (GB 38031-2020), what early warning must the Battery Management System (BMS) provide to the bus cabin before thermal runaway occurs?

1. The system must issue an acoustic and optical thermal runaway warning signal to the driver at least 5 minutes before smoke, fire, or explosion occurs, allowing safe passenger evacuation
2. The system only warns after the battery has completely burned out
3. The system sends an email to the manufacturer within 24 hours without alerting the driver
4. The system automatically ejects the battery pack onto the roadway