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6 6 K CUPS OF COFFEE CUPS OF COFFEE 3 N N 2 M 2 3 5 2 3 5 6 DONUTS DONUTS Refer to Figure 2-4, Graph (a) and Graph (b) . A shift of the economy's production possibilities frontier from Graph (a) to Graph (b) could be caused by Oa. an improvement in donut production technology. Ob. an improvement in both donut and coffee production technology. Oc. unemployment. Od. an improvement in coffee production technology