Final answer:
The elevation of the seafloor at mid-ocean ridges depends on tectonic activity.
Step-by-step explanation:
The correct answer is D) Depends on tectonic activity. The elevation of the seafloor depends on the activity of the tectonic plates at mid-ocean ridges. Mid-ocean ridges are formed by the divergence of tectonic plates, where molten rock rises to fill the gap created by the separating plates. This results in the creation of new oceanic crust and an elevated seafloor.