Explanation: Resource pooling serves as the biggest challenge to using DLP solutions to protect data at rest because data is spread across large systems, which are also shared by many different clients. With the data always moving and being distributed, additional challenges for protection are created versus a physical and isolated storage system. Portability is the ability to easily move between different cloud providers, and interoperability is focused on the ability to reuse components or services. Reversibility pertains to the ability of a cloud customer to easily and completely remove their data and services from a cloud provider.