Final answer:
The most gradual change in slope in the ocean is found at the continental shelf, which extends from the shoreline to the shelf break. This area has the least steep gradient compared to other parts of the ocean.
Step-by-step explanation:
The most gradual change in slope in the ocean can be found at the (c) continental shelf. The continental shelf is the submerged portion of continent crust in relatively shallow water, extending from the shoreline to the drop-off point marked by the shelf break. This area represents the least steep gradient as it transitions from the land to the deeper parts of the ocean, in contrast to areas like the continental rise, abyssal plains, deep ocean trenches, and mid-ocean ridges, which have steeper slopes or more abrupt changes in topography.
During periods known as lowstands, when the relative sea level is low, the continental shelf and adjacent carbonate platforms are exposed, allowing extensive deltas to form at the margin. It is during such times that a significant amount of sediment can be transported into deep marine basins. This shelf environment is dynamic and crucial for various marine ecosystems, such as coral reefs, which are typically found in shallow ocean waters adjoining the continental shelf.