Segregation of duties is a key control for preventing and detecting fraudulent transactions, especially in a large organization where there are many employees and transactions involved. Segregation of duties means that no single person has the authority or ability to initiate, approve, execute, and record a transaction without the involvement or oversight of another person. This reduces the opportunity and incentive for fraud, as well as the risk of errors or omissions. Segregation of duties also facilitates the detection of fraud by creating an audit trail and increasing the likelihood of whistleblowing.

The other options are not as effective as segregation of duties for mitigating risk related to fraudulent transactions. Monetary approval limits (B) are useful for controlling the amount and frequency of transactions, but they do not prevent unauthorized or fraudulent transactions from occurring. Clear roles and responsibilities © are important for defining the expectations and accountabilities of employees, but they do not ensure that employees comply with them or that their actions are monitored and verified. Password policies (D) are essential for securing access to systems and data, but they do not prevent fraudsters from exploiting weak or compromised passwords or from using legitimate passwords for fraudulent purposes.