When securing palletized heavy goods on an open flatbed cargo truck, which of the following restraint practices is required under PRC Road Freight Transport Safety Regulations?

1. Using certified ratchet tensioners, tie-down straps, and high-friction rubber dunnage mats across all cargo units
2. Relying solely on the vehicle's side dropsides without additional top-over lashings
3. Securing only the rearmost pallet and leaving intermediate pallets free to settle naturally
4. Tying cargo exclusively with natural hemp ropes secured directly to the wheel rims