Indicate whether each of the following is a product cost or a period cost:

3.1. Electricity for lighting a factory building =

3.2. Costs of delivering finished bicycles to dealers =

3.3. Cost of a store detective in a retail establishment =

3.4. Cost of eggs in a bakery =

3.5. Cost of chocolate to a candy manufacturer =

3.6. Salary of injection molding machine operator in a plastics factory =

3.7. Salary of a sewing machine operator in a clothing factory =

3.8. Depreciation of a freezer in an ice cream plant =