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.

The recovery time objective (RTO) is a measure of the amount of time it would take to recover operations in the event of a disaster to the point where management's objectives are met for BCDR.

Explanation
To implement DNSSEC, no additional changes are needed to applications or their code because the integrity checks are all performed at the system level.

A limit puts a maximum value on the amount of resources that may be consumed by either a system, a service, or a cloud customer. It is commonly used to prevent one entity from consuming enormous amounts of resources and having an operational impact on other tenants within the same cloud system.
Limits can either be hard or somewhat flexible, meaning a customer can borrow from other customers while still having their actual limit preserved. A reservation is a guarantee to a cloud customer that a certain level of resources will always be available to them, regardless of what operational demands are currently placed on the cloud environment. Both cap and throttle are terms that sound similar to limit, but they are not the correct terms in this case.