The correct answer is that a close spacing of isolines on a topographic map indicates that the gradient is steep.
Isolines, such as contour lines, are used on topographic maps to represent elevation changes over a given area. When these lines are closely spaced, it signifies that there is a rapid change in elevation over short horizontal distances. This means that the terrain is steep, as the slope increases significantly in a small area.
In contrast, when isolines are widely spaced, this indicates a gentle slope where the elevation changes gradually over a larger distance, contributing to a flatter area. Constant elevation would be represented by isolines that run parallel and are evenly spaced, not close together. The presence of water bodies is not indicated on a topographic map by the spacing of isolines, as they typically represent land elevations rather than bodies of water.