What must you do as driver of a school bus before leaving a bus stop?

Your selected combination is correct because as the driver of a school bus, it is essential to ensure the safety of children before departing from a bus stop.

1. Making sure all doors are properly closed ensures that no child can accidentally fall out or get trapped.
2. Checking for any child in front of the bus is crucial because children may not be visible to the driver, and this step helps prevent accidents.
3. Switching off the hazard warning lights signals to other road users that you are about to leave the stop and that it's safe for them to proceed.

These actions are mandated by German traffic regulations to enhance the safety of children and ensure that school bus operations are conducted safely. Adhering to these steps helps prevent accidents and ensures a smooth transition for students getting on and off the bus.