Which control is evaluated as a preventive control by an IS auditor?

The correct choice is table lookups, as this control is considered a preventive measure. Table lookups involve validating input data against predefined criteria or values stored in a lookup table before any further processing occurs. This means that erroneous, malicious, or inappropriate data can be detected and prevented from entering the system at an early stage. By effectively validating inputs, table lookups can significantly reduce the risk of data entry errors or security vulnerabilities that might arise from invalid data.

In contrast, transaction logs, before and after image reporting, and tracing and tagging primarily serve as detective or corrective controls. Transaction logs provide a record of activity after it has happened, aiding in investigations or audits, whereas before and after image reporting is focused on documenting changes for review rather than preventing them. Tracing and tagging typically relate to the identification and monitoring of assets or processes after they have occurred, rather than stopping issues before they arise. Thus, these options don't embody the preventive nature attributed to table lookups.