Roadstar Motors manufactures both gasoline$-$powered and electric$-$powered vehicles. In the last five years, gasoline$-$powered vehicles sales have declined, and electric$-$powered vehicles sales have increased but overall net income has decreased. If the descriptive question is "What factors are causing net income to decrease?", what measures can be used for this analysis?

Group of answer choices

a$.$ Production capacity for each vehicle model

b$.$ Percentage changes in ending inventory values for each vehicle

c$.$ The operating margin percentage for each year for each vehicle

d$.$ The cash flow values from financing operations from each vehicle