Choice "A" is correct. A flexible budget is a budget prepared at different levels of operating activity. It is appropriate for any activity that has variable costs. It is not necessary for the control of fixed costs since fixed costs do not vary with changes in the level of activity.Choice "c" is incorrect. Both of these budgets have variable cost components, so flexible budgets would be meaningful at different levels of activity.Choice "d" is incorrect. The marketing budget would have variable costs, making a flexible budget appropriate for control over marketing costs.Choice "b" is incorrect. The direct materials usage budget includes variable costs, making a flexible budget appropriate for control over direct material usage costs.