An organization has been experiencing issues with deleted network share data and improperly assigned permissions.

File Integrity Monitoring (FIM) is the best tool for detecting unauthorized file deletions, modifications, or improper permission changes within network shares. FIM works by creating cryptographic hashes and baselines for protected files or directories and then continuously monitoring for deviations. Any unauthorized deletion, modification, or permission change triggers alerts.

Security+ SY0-701 identifies FIM as a foundational integrity control used in compliance frameworks (PCI-DSS, HIPAA) and operational security monitoring. Because the organization is experiencing unpredictable changes to shared files and permissions, FIM provides visibility and accountability for who changed what and when.

DLP (A) prevents data leakage but does not detect permission changes. EDR (B) focuses on endpoint threat behavior, not file integrity on network shares. ACLs (D) define permissions but do not track changes or detect unauthorized modifications.

Therefore, C: FIM is the correct choice.