Answer:
plateau
Step-by-step explanation:
Let's see the possible answers:
hill : No. A hill is a relatively small and round relief on a normally flat area. Not the case here... especially since the question mentions a low-relief.
mountain : No. A mountain is a big relief, much bigger than a hill... with steep sides and a summit... again, nothing like a low-relief.
plains : No. Although plains are also flat, they are low-elevation, think about fields for growing crops.
plateau: Yes. A plateau is a relatively flat (low-relief) that is significantly elevated compared to its surroundings. Drops from a plateau is usually the best scenario for a waterfall, like on this picture.