In the Graph Below Six Short-Run Average Cost Curves Labeled

In the graph below six short-run average cost curves labeled a through f are illustrated.

-Refer to the graph above to answer this question.Which set of short-run average cost curves illustrates economies of scale?

A) a and b only
B) a,b and c only
C) a,b,c,and d
D) d and e only
E) e and f only.