Surface runoff happens when, usually a liquid, flows from a high point to a low point because of a driving force in pressure difference as evident in the difference in elevation. In other words, liquid will runoff from the mountains to the plains. Since a low, flat plain has no difference in elevation, it will not cause the fluid to flow. Thus, it is impossible for surface runoff to happen within a low, flat plain.
13 is the answer. Mean means average. Add up all of your numbers to get 130 then divide by the numbers you have so 130/10 you get 13.
Do you actually mean when?
Answer: The formation of elements heavier than iron and nickel requires the input of energy. Supernova explosions result when the cores of massive stars have exhausted their fuel supplies and burned everything into iron and nickel. The nuclei with mass heavier than nickel are thought to be formed during these explosions.
Explanation:
