When can you safely return to the right-hand lane after overtaking another vehicle?

The correct answer is determined by the principle of ensuring safe driving practices after overtaking another vehicle. You can safely return to the right-hand lane after you can clearly see the overtaken vehicle in your rearview mirror. This indicates that you have passed the other vehicle sufficiently, allowing for a safe margin and reducing the risk of an accident involving the vehicle you have just overtaken.

Successfully spotting the overtaken vehicle in your rearview mirror provides reassurance that you have enough distance between your vehicle and the one you passed, indicating that it is now safe to merge back into the right lane. This practice is crucial in maintaining safe driving environments and preventing collisions.

The other options are less reliable as indicators of safe lane change. For example, passing a mile marker does not provide any information about the position or proximity of the overtaken vehicle. Hearing the horn may not be a safe indicator since it can be misunderstood or signal different intentions from the other driver. Lastly, merely waiting for the road to be clear can overlook the necessity of ensuring proper distance from the overtaken vehicle before returning to the lane.