Jones Corporation incurred the following costs during the year: Manufacturing plant rent $40,000 Sales office electricity 5,000 Depreciation of sales manager's car 3,000 Nonrefundable theater tickets 2,000 Assembly workers' wages 14,000 Indirect labor 6,000 a. Which, if any, of the above are product costs? b. Which, if any, of the above are period costs? c. Which, if any, of the above are sunk costs?