The managers of Financial Burden Ltd are analysing some of their corporate costs to determine the cost of each department's use of administrative services. The accountant wants to allocate the costs of payroll processing using an activity-based costing system. The most appropriate cost driver for the payroll processing cost pool is the:

a. number of pay periods each month.

b. current tax rate for employees.

c. total number of deductions from an individual employee's pay.

d. number of employees