The correct answer is: A. a predetermined rate
A predetermined rate is a rate that is set in advance of the period to which it applies. It is used to estimate the amount of overhead that will be incurred in the period. The rate is calculated by dividing the budgeted overhead by the budgeted activity base. The activity base is the factor that is used to measure the amount of activity that occurs in the period.
The actual overhead expenses are the actual costs that are incurred in the period. They are determined by adding up the actual costs of all the overhead items.
The charged overheads are the amount of overhead that is charged to the products or services that are produced in the period. The charged overheads are calculated by multiplying the predetermined rate by the actual activity base.
The actual overhead expenses may be different from the charged overheads if the actual activity base is different from the budgeted activity base. For example, if the actual production volume is higher than the budgeted production volume, then the actual overhead expenses will be higher than the charged overheads.
The actual overhead expenses may also be different from the charged overheads if the actual overhead costs are different from the budgeted overhead costs. For example, if the actual cost of electricity is higher than the budgeted cost of electricity, then the actual overhead expenses will be higher than the charged overheads.