The system only allows payments to vendors who are included in the system’s master vendor list is an example of a preventative control in an accounts payable system. A preventative control is a control that aims to prevent errors or irregularities from occurring in the first place. By restricting payments to vendors who are authorized and verified in the master vendor list, the system prevents unauthorized or fraudulent payments from being made. The other options are examples of other types of controls, such as backup (recovery), reconciliation (detective), and communication (directive) controls. References: CISA Review Manual, 27th Edition, page 223