If a neutral atom of beryllium has 4 protons and 5 neutrons, what is the mass number of the atom?

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:

d) varies at diffrent times during trip