正解:D
A false negative is a security incident that was not detected by the SIEM system, which presents the greatest risk as it allows attackers to compromise the organization's assets and data without being noticed or stopped.
A high number of false negatives can indicate that the SIEM system is not configured properly, has insufficient data sources, or lacks effective analytics and correlation rules. (From CISM Review Manual 15th Edition) References: CISM Review Manual 15th Edition, page 181, section 4.3.2.4.