When coupling a tractor unit to a semi-trailer, what is the crucial visual check that must be performed under the fifth wheel (sellette d'attelage)?

1. Verify with a flashlight that the locking jaws (mâchoires de verrouillage) have completely closed around the kingpin (cheville ouvrière) and the safety release lever is locked
2. Check that the fifth wheel plate is completely dry without any grease
3. Check that the trailer landing gear legs are touching the ground
4. Verify that the rear mudguards have been removed