Consider this graph. Gizmos 10 9 8 7 6 4 3 2 1 4 5 6 7 8 9 10 Widgets What best explains the shape of the production possibility frontier in the graph? 0 1 2 3 O a. Some resources used to produce one of the goods are not as productive when they are used to produce the other good. O b. Producers can move from one point to another on the production possibilities frontier in response to consumers' demands. c. The production of widgets and gizmos require the same resources to produce. d. This economy has the capacity to produce different combinations of widgets and gizmos.