Steel Works Inc., incurred the following costs during May: 1. Depreciation of office equipment 2. Advertising expense 3. Cost of factory maintenance 4. Utility expense of administrative offices. 5. Salary of assembly line workers 6. Salary of the president Which of these costs would be classified as period costs? O 1,2,4,6 1,2,6 2,3,6 O 1,4,5