Final answer:
The horizon should generally be in the middle of the side mirror, closer to the top, to ensure a proper field of vision and minimize blind spots while driving.
Step-by-step explanation:
When adjusting your side mirrors, the correct position for the horizon is typically c) in the middle of the mirror, but it generally should be closer to the top. This ensures a proper field of vision when driving, which includes the road, the horizon, and any vehicles or obstacles around you. The horizon should not be at the very top or bottom, as this could limit your ability to see traffic. Moreover, for an average-height driver, the side mirrors should be adjusted so that the horizon (or a distant object at the same height) appears roughly in the center of the mirror, with a slight bias toward the top. This adjustment minimizes blind spots and maximizes visibility.