Refer to the information provided in Table 8.7 below to answer the questions that follow. Table 8.7 All Figures in Billions of Dollars Aggregate Output Aggregate Consumption Planned Investment 200 300 100 400 450 100 600 600 100 800 750 100 1,000 900 100 Refer to Table 8.7. At an aggregate output level of $600 billion, the unplanned inventory change is Select one: a. $0. b. -$100 billion. c. -$50 billion. d. $50 billion