Contour interval on a map sheet denotes
(a) Vertical distance of contour lines above the datum plane
(b) Vertical distance between two successive contour lines
(c) Slope distance between two successive contour lines
(d) Horizontal distance between two successive contour lines
(a) Vertical distance of contour lines above the datum plane
(b) Vertical distance between two successive contour lines
(c) Slope distance between two successive contour lines
(d) Horizontal distance between two successive contour lines