You're securing 20 drums of a Class 3 flammable liquid on a flatbed. Which statement correctly distinguishes blocking from bracing?

AAMVA CDL Manual, Section 3 – Transporting Cargo Safely, Sec. 3.3.1 'Blocking and Bracing' (nhcdm.pdf p.3-1); general cargo securement duty, 49 CFR 393.100-393.136

Knowing the difference between blocking and bracing isn't academic. A load that's only blocked against forward sliding can still tip in a turn, crack a drum, and trigger a citation or a spill. Proper securement means addressing movement in every direction the vehicle can throw at the cargo.