An internal service fund is used to account for goods or services provided by one department or agency to other departments or agencies of the governmental unit, typically on a cost-reimbursement basis.

To establish accurate billing rates (e.g., hourly rates), the fund must use actual costs of providing services. This includes materials consumed, labor, depreciation, and overhead. Materials purchased but not used should not be included in the rate calculation for the current period.

Relevant Standards and References:

FASAB SFFAS No. 4, Managerial Cost Accounting

GASB Codification Section 1800, Internal Service Funds

GFOA Best Practices – Internal Service Fund Rate Setting

Therefore, Option A is correct.