Which of the following are true: A) A. planning budget is prepared before a period begins and is valid for only the planned level of activity. B) A flexible budget is an estate of what revenues and costs would have been, given the actual level of activity for the period. C) A spending variance is the difference between the actual amount of the cost and how much a cost should have been given the standard level of activity. D) A revenue variance is the difference between the actual total revenue and what the total revenue should have been given the actual level of activity for the period. C and D only A,B,C and D A,B and D only B and D only