4
Fe
(
III
)
+
3
O
2
→
2
F
e
2
O
3

answer; i do believe the correct answer is (river); /// good luck

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.