You are to drive a motor vehicle with which you are unfamiliar. Why do you have to be particularly careful to begin with?

The selected combination is correct because when driving a motor vehicle that you are not familiar with, it's essential to be cautious about three key aspects:

1. **Arrangement and Function of Controls**: Understanding how the controls are laid out and how they work is crucial for safe operation. If the controls are not intuitive or differ from what you are used to, it could lead to unsafe driving and potential accidents.

2. **Braking Characteristics**: Different vehicles have different braking systems and characteristics. Knowing how the vehicle responds when you apply the brakes is crucial to maintain control, especially in emergency situations.

3. **Manoeuvrability**: Each vehicle has unique handling and maneuverability. Being aware of how the vehicle turns, accelerates, and responds to steering inputs is vital for navigating safely, particularly in tight spaces or during complex driving scenarios.

According to German traffic regulations, it is emphasized that drivers should be fully familiar with the vehicle they are operating to ensure safety on the road. This knowledge reduces the risk of accidents and enhances the driver's ability to respond to unexpected situations.