The correct answer is D - Implementation of data encryption.
As per WGU Cybersecurity Architecture and Engineering (KFO1 / D488), encrypting data at rest ensures that even if attackers breach the system and obtain files, the data remains protected because it cannot be easily read without decryption keys.
Firewall enforcement (A) restricts access but does not protect data if stolen. Disabling printing services (B) limits data leakage but not core data protection. Backups (C) help with recovery, not immediate breach protection.
Reference Extract from Study Guide:
"Encrypting sensitive data ensures confidentiality even in the event of a security breach, protecting information from unauthorized exploitation."
- WGU Cybersecurity Architecture and Engineering (KFO1 / D488), Data Security and Encryption Practices