When coupling, trailer height should `_________`.

A Be low enough so that it is raised slightly when the tractor is backed under it.

explanation

The trailer should be low enough that it is raised slightly by the tractor when the tractor is backed under it. Raise or lower the trailer as needed. (If the trailer is too low, the tractor may strike and damage the nose of the trailer; if the trailer is too high, it may not couple correctly.)