The primary difference between a fixed budget and a flexible budget is that a fixed budget

a.cannot be changed after the period begins, whereas flexible budget can be changed after the period begins.

b.is concerned only with future acquisitions of fixed assets, whereas a flexible budget is concerned with expenses that vary with sales.

c.includes only fixed costs, whereas a flexible budget includes only variable costs.

d.is a plan for a single level of production, whereas a flexible budget can be converted to any level of production.