Which of the following statements is true?

Using a flexible budget, actual results can be compared to what costs should have been at the actual level of activity.

Fixed costs should not be included in a flexible budget because they do not change when the level of activity changes.

Actual costs are determined by plugging the actual level of activity for the period into the cost formulas used in flexible budgets.

Fixed costs should not be ignored when evaluating how well a manager has controlled costs.