When can mirror adjustment be checked properly?

The correct answer highlights the importance of setting mirrors when the trailer is straight in relation to the vehicle. This is crucial because it ensures that the driver has a clear and accurate view of the surrounding environment, particularly the areas alongside and behind the vehicle. When the trailer is aligned straight, it minimizes blind spots and provides a better perspective of the distances to other vehicles or objects. Adjusting mirrors in this orientation helps ensure that the driver can see any potential hazards and adjust their driving accordingly.

Adjustments made while the vehicle is moving could be dangerous, as it distracts the driver and could lead to accidents. Checking mirrors while parked in a garage may not reflect real-world conditions, as the vehicle may be in a confined space lacking the broader visibility required for safe driving. Furthermore, adjusting mirrors only when the vehicle is loaded is not ideal, as each load can shift the position of the trailer, necessitating a reassessment of mirror angles to ensure safety at all times, regardless of whether the vehicle is loaded or empty.