When is it safe to return to your lane after passing another vehicle on a two-lane road?

The correct choice is based on the principle of ensuring that it's safe to merge back into your lane without endangering yourself or other drivers. When you can see both headlights of the vehicle you have just passed in your rearview mirror, it indicates that you have successfully cleared the vehicle and that there is enough distance between your vehicle and the one you have passed. This observation means the other driver is far enough behind you that it is safe for you to return to your lane.

This practice is essential for maintaining safe distances and preventing any collisions during the passing maneuver. It ensures that the vehicle you passed is not in a position to impede your return to the lane. In contrast to the other options, focusing on your passenger side mirror or the empty space directly next to you does not provide a definitive measure of safety as they do not take into account the distance of the vehicle from your position. Seeing headlights from your rearview mirror specifically confirms that the other vehicle is behind you and adequately distanced.