Which of the following statements is correct regarding marketing return on investment $($ROI$)?$

A$.$ The benefits of ROI are short$-$term only.

B$.$ Marketers today spend freely and are less concerned with ROI.

C$.$ There is currently no consistent definition of marketing ROI.

D$.$ ROI is measured by dividing sales by outstanding debt.

E$.$ Measuring ROI is an extremely easy task.