Cloud services make exclusive use of virtualization, and systems change over time, including the addition, subtraction, and reimaging of virtual machines. It is extremely unlikely that the exact same virtual machines and images used in a previous audit would still be in use or even available for a later audit, making the tracking of changes over time extremely difficult, or even impossible. Elasticity refers to the ability to add and remove resources from a system or service to meet current demand, and although it plays a factor in making the tracking of virtual machines very difficult over time, it is not the best answer in this case. Resource pooling pertains to a cloud environment sharing a large amount of resources between different customers and services. Portability refers to the ability to move systems or services easily between different cloud providers.

Upon successful authentication, the identity provider sends an assertion with appropriate attributes to the relying party to grant access and assign appropriate roles to the user. The other terms provided are similar sounding to the correct term but are not actual components of a federated system.

Explanation/Reference:
Explanation:
The Uptime Institute publishes the most commonly used and widely known standard on data center tiers and topologies. It is based on a series of four tiers, with each progressive increase in number representing more stringent, reliable, and redundant systems for security, connectivity, fault tolerance, redundancy, and cooling.