When securing a heavy wheeled vehicle (such as a tractor or front-end loader) onto a flatbed trailer, what is the minimum securement required under NSC Standard 10?

1. Two tiedowns, one at the front and one at the back
2. Four tiedowns attached directly to the vehicle's frame, plus wheel chocks or blocks to prevent rolling
3. Ropes tied around the tires
4. No tiedowns are needed if the vehicle's parking brake is applied