A data loss prevention (DLP) tool implemented in monitor mode only observes and logs potential data leakage but does not actively prevent it. This leaves the organization vulnerable to data breaches, making it the most critical concern in a pre-implementation review. * Crawlers for Sensitive Data (Option B):While crawlers may pose a performance impact, they are essential for discovering sensitive data. * Deep Packet Inspection (Option C):Though it introduces privacy considerations, it is a standard DLP functionality for inspecting data in transit. * Encryption Key Management (Option D):While important for security, improper management does not immediately prevent DLP functionality. Reference:ISACA CISA Review Manual, Job Practice Area 4: Protection of Information Assets.