A retina scan could be used in conjunction with an RSA token because it is a biometric factor, and thus a different type of factor. An access card, RFID, and USB thumb drive are all items in possession of a user, the same as an RSA token, and as such would not be appropriate.

Explanation
Volume storage works as a virtual hard drive that is attached to a virtual machine. The operating system sees the volume the same as how a traditional drive on a physical server would be seen.

Reversibility is the cloud concept involving the ability for a cloud customer to remove all of its data and IT assets from a cloud provider. Also, processes and agreements would be in place with the cloud provider that ensure all removals have been completed fully within the agreed upon timeframe. Portability refers to the ability to easily move between different cloud providers and not be locked into a specific one.
Removability and extraction are both provided as terms similar to reversibility, but neither is the official term or concept.

Explanation/Reference:
Explanation:
DLP can be combined with DRM to protect intellectual property; both are designed to deal with data that falls into special categories. SIEMs are used for monitoring event logs, not live data movement. Kerberos is an authentication mechanism. Hypervisors are used for virtualization.