When a heavy truck breaks down and must be parked on a steep mountain incline, what is the mandatory sequence of mechanical securing actions?

1. Engage the spring parking brake, shift into reverse (facing downhill) or 1st gear (facing uphill), place wheel chocks (三角木/轮楔) downhill from tires, and angle steering wheels toward the curb/bank
2. Leave the transmission in neutral, leave the parking brake disengaged, and rely solely on loose gravel behind tires
3. Jack up the drive axle and place the truck on wooden blocks in the travel lane
4. Keep the service brake pedal depressed with a wooden stick while leaving the cab unattended