Mass number is O the average atomic mass of an element.
O the total number of electrons in an atom of an element.
O the total number of protons in an atom of an element.
O the total number of protons and neutrons in an atom of an element.

4 th is the answer

tracks, burrows, eggshells, nests, tooth marks, or gastroliths

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: