Option 1:
Option 2:
ISOFIX + 3-point belt
3-point belt
Make sure the belt runs under the seat belt guide.
Make sure when you're using the car 3-point-belt, that the belt doesn't
interfere with the main load-bearing contact point of the carseat.
Make sure that with both options the safety seat is positioned as closely as
possible to the back of the car seat.