The gently sloping submerged surface that extends from the shoreline toward the ocean basin floor is the continental

shelf.

Explanation:

The image attach, which you can find on internet with license to be reused, shows the shelf along with other surfaces from shore through the ocean.

The continental shelf is the landmass that is underwater next to the shore, it extends from the continent and comprisses an area of shallow water (the shelf sea)

Aslo, there is the shelf surrounding an island which is known as an insular shelf.

After the shelf you find a steep continental slope, followed by the flatter continental rise, and then the abyssal plain (the deepest surface).

Depending on how the continental plates move it can cause a continental scale shift.

Letter a, because when there are unlike charges they will always attract to each other.