Where is the permitted to untie tools or a trailer from the tractor?

1. On a cement or asphalt surface only.
2. Everywhere. The surface condition in not important.
3. On an inclined plane, to make it easier for the harnessed tool.
4. Correct answer: On a leveled surface, to prevent accidental movements.

WhyTools and trailers are unhitched on level ground so they do not roll away.