Which of the following statements is True regarding product and period costs? O a. Office salaries expense is a product cost and factory maintenance is a period cost. O b. Office rent is a product cost and supervisors' salaries expense is a period cost. O c. Sales commissions is a product cost and indirect labor is a period cost. O d. Factory rent is a product cost and advertising expense is a period cost. O e. Delivery expense is a product cost and indirect materials is a period cost