A firm within the defense industry has been directed to comply with contractual requirements for encryption of a government client's Controlled Unclassified Information (CUI). What encryption strategy represents how to protect data at rest in the MOST efficient and cost-effective manner?

A、 Perform logical separation of program information, using virtualized storage solutions with encryption management in the back-end disk systems
B、 Perform logical separation of program information, using virtualized storage solutions with built-in encryption at the virtualization layer
C、 Perform physical separation of program information and encrypt only information deemed critical by the defense client
D、 Implement data at rest encryption across the entire storage area network (SAN)