Classify each cost of a paper manufacture as either a product cost or a period cost:

1. Salaries of scientists studying ways to speed forest growth.
2. Cost of computer software to track WIP Inventory.
3. Cost of electricity at the paper mill.
4. Salaries of the company's top executives.
5. Cost of chemicals to treat the paper.
6. Cost of TV ads.
7. Depreciation on the manufacturing plant.
8. Cost to purchase wood pulp.
9. Life insurance on the CEO.