What is the correct and safe driving practice when operating a heavy truck down a long, steep mountain gradient?

1. Select a low gear in advance to utilize engine compression braking and auxiliary retarders, avoiding continuous heavy friction braking
2. Shift the transmission into neutral (空挡) and rely entirely on the service foot brake pedal
3. Turn off the engine ignition key to save fuel while steering with muscle force
4. Maintain maximum speed in high gear and apply the emergency handbrake continuously