Which of the following statements about a static budget is true?

a$.$ A static budget is prepared by first identifying the relevant activity level and then adjusting for the actual level.

b$.$ A static budget helps in comparing actual costs to the budgeted costs for actual activity levels.

c$.$ A static budget shows the expected results of a responsibility center for only one activity level.

d$.$ A static budget is a series of flexible budgets for different levels of activity.