What safety check must a driver perform immediately after coupling a tractor to a semi-trailer before raising the landing gear?

1. Perform a 'Pull Test' (Anfahrprobe) by gently attempting to pull forward in low gear against the trailer brakes, visually verify that the fifth wheel locking bar is fully engaged across the kingpin, and secure the safety latch
2. Raise the landing gear first, then rely on the dashboard trailer symbol without a pull test or visual check
3. Connect the air and electrical lines and assume the kingpin is locked if no warning appears
4. Perform only a pull test; a visual check of the locking mechanism and safety latch is unnecessary