One way in which the ancient Sumerians, Egyptians, and Mayas are similar is that these civilizations developed irrigation systems.
Answer:
Graphs show a pattern in something that we are following. So by using those patterns on the graphs, we can see how the process that we are following is changing and we can conclude that without anything drastic happening the process will continue with the same pattern.
An example would be a pattern in weight loss. If a graph shows that a person is losing weight 1 pound per week we can conclude that the next week the person will have 1 pound less. This will only change if the person starts eating more which would be a drastic change to the pattern.
The plow :)
Hope this helps