Which of the following best describes a flexible budget?

A A budget which is designed to be easily updated to reflect recent changes in unit costs or selling prices B A budget which can be flexed when actual costs are known, to provide a realistic forecast for the forthcoming period C A budget which, by recognising different cost behaviour patterns, is designed to change as the volume of activity changes D A budget which is prepared on a spreadsheet, with the flexibility to add new costs items to prepare new forecasts as circumstances change during the year