Seafloor spreading occurs along mid-ocean ridges. The process of seafloor spreading involves the continuous movement and separation of tectonic plates, where new oceanic crust is formed at the mid-ocean ridges. As magma rises from the mantle and cools, it solidifies to create new oceanic crust, pushing the existing crust away from the ridge in opposite directions. This process contributes to the expansion of ocean basins and the creation of new seafloor. Therefore, the correct answer is "mid-ocean ridges."
Seafloor spreading primarily occurs along mid-ocean ridges, not ocean basins, ocean trenches, or fault lines.
