______ are extensive plains that lie between the continental margins and mid-ocean ridges.

Abyssal plains are extensive, flat regions of the ocean floor that lie between the continental margins (where the ocean depth increases rapidly) and the mid-ocean ridges (where new oceanic crust is formed). They are among the flattest and smoothest regions on Earth, covered by fine-grained sediments. The other options are not standard geomorphological terms for ocean floor features.