Why are input and output good words to use when discussing systems?

Hey there "Minabear" but I think that the answers for this one is that the occurences that changed over the the 30 year period changed because it is now lower than the previous years at the beginning, so basically the occurance changed to being occuring more frequently from the year 1950 to changing to a lower rate of occuring frequency at the end of the graphs years which is 1980 Explanation: The graph is defnintley decreasing from the start of the graph (1950) all the way to the end of the graph (1980), and i am also taking the same project assignment on edge.