Prunedale Co. uses a periodic inventory system. Beginning inventory on January 1 was understated by $30,000, and its ending inventory on December 31 was understated by $17,000. In addition, a purchase of merchandise costing $20,000 was incorrectly recorded as a $2,000 purchase. None of these errors were discovered until the next year. As a result, Prunedale's cost of goods sold for this year was:
a. Overstated by $31,000.
b. Overstated by $5,000.
c. Understated by $31,000.
d. Understated by $48,000.