What type of graph is proper to use when comparing two continuously changing variables?

A line graph is ideal for comparing two continuously changing variables because it effectively shows trends over time or the relationship between the variables. In a line graph, data points are plotted along a grid and connected by lines, which allows for visual analysis of how one variable affects the other as both change.

This format is particularly useful when tracking changes across intervals, as it highlights the continuity and the rate of change in both variables. For example, if one variable represents time and the other represents temperature, a line graph can clearly illustrate how temperature rises and falls over that time period.

While bar graphs are effective for categorical data comparisons, and pie charts are used to represent parts of a whole for categorical data, they do not convey the nuances of continuously changing variables. Scatter plots can also be used to illustrate relationships between two variable sets, but they do not inherently show the change over an interval like a line graph does. Thus, the line graph is the best choice in this situation.