Before backing a tractor under a trailer to couple, why should the trailer's parking brakes be set?

Pick an answer

1. It's only needed on a downhill grade, never on flat ground
2. So the trailer cannot roll while the tractor is positioning underneath it
3. It makes the fifth wheel lock automatically once contact is made
4. Setting the brakes has no real purpose before coupling, it's just habit

Correct!

Not quite. The correct answer is highlighted.