Which feature of the ocean floor is described as a deep, steep-sided canyon?

The correct answer is trench because oceanic trenches are characterized as deep, narrow depressions in the ocean floor, and they are often steep-sided, resembling canyons in their formation. These trenches are formed by the process of subduction, where one tectonic plate moves under another and sinks into the mantle, leading to the creation of deep and narrow valleys. The Marianas Trench, for instance, is the deepest known oceanic trench in the world and exemplifies these steep sides and significant depth.

In contrast, while a valley can refer to a low area between hills or mountains, it is not specific to the ocean floor and does not imply the same depth or steepness as a trench. A canyon, while it may suggest similar features, often refers to a landform on the Earth's surface, typically formed by erosion, rather than a deep underwater structure. A gulf refers to a large area of sea partially enclosed by land and does not relate to steep-sided geological formations on the ocean floor.