Answer: a. True - The scattergraph method is easy to understand and apply.
Explanation:
This is the simplest and most straight-forward statement that is universally true about the scattergraph method. The other options have elements of truth, but they also have limitations or qualifications. For example, while it is true that the scattergraph method is not as precise as some other methods (option b), and that it can reveal quirks in cost behavior (option d), these aren't necessarily defining characteristics of the scattergraph method. And option c is generally false, as scattergraphs use all data points, not just two.