In which direction should the y-axis run?

The correct choice indicates that the y-axis should run vertically. In a standard Cartesian coordinate system, the y-axis represents the vertical direction, allowing for the representation of values that can increase or decrease as you move up or down on the graph. The vertical orientation of the y-axis is crucial for accurately plotting data, particularly when it comes to visualizing relationships between variables, such as in scientific graphs, charts, or data representations in various fields, including veterinary medicine. This setup facilitates easier reading and interpretation of trends and comparisons, since the x-axis typically represents the horizontal direction and the y-values provide essential information about the dependent variable.