Here's a breakdown of the locations:

* Mid-ocean ridges: These are underwater mountain ranges where new oceanic crust is formed.

* Deep ocean basins: These are vast, flat plains that cover the majority of the ocean floor.

Abyssal hills are essentially small, rounded mountains that are scattered across the deep ocean basins. They are formed by volcanic activity and tectonic processes that occur along mid-ocean ridges. As new crust is created, it pushes away from the ridge, cools and contracts, forming these hills.