What should be noted when changing a tyre using a car jack?

The selected combination is correct because both points address crucial safety aspects when changing a tyre.

1. Applying the car jack only at the specified positioning points ensures the vehicle's stability during the lifting process, which is necessary to prevent accidents or injuries when working underneath a car.

2. Ensuring the ground surface is stable and skid-resistant is vital for the jack's integrity. If the surface is unstable, there's a risk that the jack may slip, which could lead to the vehicle falling and causing harm.

Both of these factors align with German traffic safety regulations that aim to ensure safe practices when performing maintenance on vehicles. Understanding and adhering to these guidelines is essential for personal safety and the safety of others on the road.