What causes avoidable noise?

The selected combination is correct because both actions listed contribute to avoidable noise. In German traffic laws, causing unnecessary noise is discouraged as it can disturb residents and the environment. Sounding the horn as a greeting is unnecessary and can be considered noise pollution, while slamming doors shut creates excessive noise that could be avoided with careful handling.

It's essential to recognize that all actions contributing to noise disturbance should be minimized to respect the peace in residential areas and comply with regulations geared toward reducing environmental impact.