Choice "C" is correct. By vouching to time card data, the auditor is testing the occurrence assertion for hours worked.
Choice "b" is incorrect. Vouching to approved clock card data would provide evidence about hours worked, not pay rates. Pay rates would be tested by comparing to personnel records.
Choice "a" is incorrect. Vouching to approved clock card data does not provide evidence about segregation of duties.
Choice "d" is incorrect. Vouching to approved clock card data does not provide evidence about internal controls related to unclaimed paychecks. The auditor would need to observe a payroll distribution to evaluate these controls.