Choice "B" is correct. A direct supervisor's approval of the time cards most effectively ensures that payment is paid for work performed as the supervisor observes the employees and determines whether employees are present and working.
Choice "a" is incorrect. All employees recording arrival and departure by using the time clock does not ensure that the employees were actually present and/or working during the recorded time.
Choice "c" is incorrect. Having a payroll clerk recalculate all time cards provides assurance as to mathematical accuracy but this does not ensure that the employees actually were present and/or working.
Choice "d" is incorrect. Requiring all employees to sign their time cards does not ensure that employees actually worked or were present. An unscrupulous employee would claim that he/she worked by signing the time card when in fact he/she did not work.