3. Which of the following is a period cost? c. Salary of supervisor at factory d. Factory utilities expenses a. Direct materials b. Depreciation of office building 4. The following are examples of variable cost? a. Supervisor salary b. Fruits for soap product c. Premiums on insurance policy for factory building d. Depreciation on production machinery 5. A cost which change in proportion to change in volume activity is called a: a. Fixed cost b. Variable cost c. Mixed cost d. Opportunity cost