What are the supplementary terrain features?

The correct answer regarding supplementary terrain features is cut and fill. These features are specifically related to alterations in the landscape that occur during construction or terrain modification. Cut refers to the process of removing earth or rock from a site to lower the ground level, while fill involves adding earth or other materials to raise the ground level. These processes are integral in understanding how terrain can be manipulated and are essential in various military and engineering applications, especially when planning routes, constructing facilities, or preparing positions.

The other options encompass broader natural features rather than supplementary modifications. For instance, mountains, valleys, rivers, plateaus, basins, canyons, and cliffs are significant geographical formations, but they do not pertain to human alterations of the terrain in the same context as cut and fill. Understanding the distinction between these natural features and the supplementary modifications is crucial for effective terrain analysis and decision-making in military operations.