Which of the following can vary in size from only a few feet across to several hundred feet across in karst landscapes?

In karst landscapes, sinkholes can vary significantly in size, ranging from just a few feet to several hundred feet in diameter. A sinkhole, formed by the dissolution of soluble bedrock such as limestone, represents a depression or hole in the ground that can occur suddenly or over time. This variability in size is due to factors such as the thickness of overlying material, the erosive power of water, and geological conditions.

While caves are also a feature of karst landscapes, they generally have a more restricted size range compared to sinkholes and are typically characterized by complex networks of underground passages. Rills are small, shallow channels formed by surface runoff and do not reach the substantial sizes that sinkholes can. Wetlands can cover large areas as well but do not form specifically through the dissolution processes that define sinkholes. Therefore, it is the sink that distinctly aligns with the described size variability in karst terrains.