slope is the ratio of the vertical and horizontal changes between two points on a surface or a line. The vertical change between two points is called the rise, and the horizontal change is called the run.
Step-by-step explanation:
To know the horizontal change between two points you need to know the two points.
It cannot be line a or line d because the line will have a constant rate of change. It cannot be line c because line c would be undifined. Therefore, it must be line b.
