Option 1, Benchmarks, refers to fixed points on the ground used as references for measuring elevation and slope. They are marked with a distinctive symbol on a map, but they do not represent the actual lines showing slope.

Option 2, Contours, is the correct answer. Contour lines are lines drawn on a map that connect points of equal elevation. They depict the shape of the land and help visualize the slope and steepness of the terrain. Contour lines that are closer together indicate steeper slopes, while lines that are further apart show gentler slopes.

Option 3, Form lines, are not commonly used in cartography. They could refer to lines that represent the form or shape of a feature on a map, but they do not specifically indicate slope.

Option 4, Hachure, indicates the representation of slope by using short lines or hatch marks. However, disconnected lines are not typically used for this purpose, so the correct answer should be option 2, Contours.