fraud perpetuated by payroll clerk

During the year, it was discovered that a payroll clerk had been setting up fictitious employees on the payroll system with the wages being paid into the clerk’s own bank account. This clerk has subsequently left the company but you are concerned that additional frauds may have taken place in the wages department due to a lack of adequate and effective internal controls.

Which of the following additional controls is most effective at preventing fraud of this type occurring again?
1. An exception report should be generated when standing data is changed in the payroll system which is reviewed by the payroll manager
2. On a regular basis department managers should be given a list of employees for their department from the payroll system to check
3. The people working in the payroll department should not be related
4. The finance director should compare the total payroll cost each month to prior month
to identify significant differences

even after two guesses i would have not guessed that the right answer was option 3! There’s absolute no mention of 2 people colluding to perpetuate this fraud, so then why is the answer option 3 ma’am?

I thought options 1 and 2 made good deal sense, but my kit seems to suggest that they will detect fraud only after it has occurred! I find this ludicrous!! everywhere in control recommendations throughout the IC section B questions we suggest the 1st method, only to know the control is a toothless tiger!

can you pls explain maam why 3 is right and 1 and 2 are wrong?