Which of the following control activities would most likely allow for a reduction in the scope of the auditor's tests of depreciation expense?

a. Review and approval of the periodic equipment depreciation entry by a supervisor who does not actively participate in its preparation.

b. Comparison of equipment account balances for the current year with the current-year budget and prior-year actual balances.

c. Review of the miscellaneous income account for salvage credits and scrap sales of partially depreciated equipment.

d. Authorization of payment of vendor's invoices by a designated em- ployee who is independent of the equipment-receiving function.