What is the key difference between a static budget and a flexible budget? A. A static budget is based on the level of output planned at the beginning of the period; a flexible budget is based on the actual unit prices in the budget period. B. A static budget is based on the level of output planned at the beginning of the period, a flexible budget is based on the actual output level in the budget period. C. A flexible budget is based on the level of output planned at the beginning of the period; a static budget is based on the actual output level in the budget period. D. None of the above