Concept:A knoll is a small, isolated, rounded hill that rises gently above the surrounding land.
Explanation:The feature marked X is a minor, separate elevation with a rounded summit.
It is not a ridge because a ridge is a long, narrow, continuous elevated crest.
It is not a plateau because a plateau is a large, flat, elevated tableland.
It is not a gorge because a gorge is a deep, narrow, steep-sided valley.
Since the marked feature is a small and detached rounded hill, it matches the definition of a knoll.
Answer:C. Knoll
