Problem: Which of the following graphical analysis options will show you changes happening over time?
A. Box plot of average Pizza delivery time of "Store 1" vs average pizza delivery time of "Store 2"
B. Histogram and Normality test for both "Store 1" and "Store 2"
C. Pareto chart of the top defects for "on time delivery"
D. Time series plot of "weekly average delivery times"