Explanation:

- Trenches: These are the deepest parts of the ocean floor and are not flat or smooth. They are narrow, but very deep, created by tectonic activity.

- Continental Slope: This is the area that connects the continental shelf to the deep ocean floor. It's steep and not flat.

- Deep Sea Plains: These are also known as abyssal plains. They are the flattest and smoothest regions on Earth, covered by layers of sediment that level the surface.

- Continental Shelf: This is the extended perimeter of each continent, which is relatively shallow but not as smooth as the deep sea plains.