Which of the following pairs of substances can be broken down chemically?
a. ammonia and iron
b. helium and argon
c. methane and water
d. potassium and lithium
e. water and carbon

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.