The correct answer is C - Implementation of encryption for all data stored in the system.
WGU Cybersecurity Architecture and Engineering (KFO1 / D488) emphasizes that encrypting data at rest ensures that even if storage systems are compromised, the data remains confidential and secure.
Password changes (A) help secure user accounts but not stored data. Firewall policies (B) and VPNs (D) protect data in transit and access control but not the storage layer itself.
Reference Extract from Study Guide:
"Encrypting data at rest ensures that stored data remains confidential and protected from unauthorized access, even if storage devices are compromised."
- WGU Cybersecurity Architecture and Engineering (KFO1 / D488), Data Protection Strategies