Which of the following statements is true? (You may select more than one answer.)

a. A planning budget is prepared before the period begins and it is based on the actual level of activity incurred during the period.

b. A flexible budget is an estimate of what revenues and costs should have been, given the actual level of activity for the period.

c. The variance analysis cycle includes analyzing differences between actual results and what should have occurred according to the budget.

d. The management by exception approach enables managers to focus on the most important variances while bypassing trivial discrepancies.