please pick ABC or D for 28,29,30

28. When using a flexible budget, a decrease in activity within the relevant range: a. Decreases variable cost per unit b. Increases variable cost per unit c. Decreases total costs d. Increases total cost 29. A budget that is based on the actual activity of a period is known as a: a. Continuous budget b. Flexible budget c. Static budget d. Master budget 30. Which of the following may appear on a flexible budget performance report? a. An unfavorable activity variance b. A favorable revenue variance c. An unfavorable spending variance d. All of the above may appear on a flexible budget performance report