Identify each of the following costs as either a product cost or a period cost.
________ 1. Factory maintenance
________ 2. Sales commissions
________ 3. Depreciation—Factory equipment
________ 4. Depreciation—Office equipment
________ 5. Rent on factory building
________ 6. Interest expense
________ 7. Office manager salary
________ 8. Indirect materials used in making goods