Explanation: Portability is the ability for a service or system to easily move among different cloud providers. This is essential for using a cloud solution for BCDR because vendor lock-in would inhibit easily moving and setting up services in the event of a disaster, or it would necessitate a large number of configuration or component changes to implement. Interoperability, or the ability to reuse components for other services or systems, would not be an important factor for BCDR. Reversibility, or the ability to remove all data quickly and completely from a cloud environment, would be important at the end of a disaster, but would not be important during setup and deployment. Elasticity, or the ability to resize resources to meet current demand, would be very beneficial to a BCDR situation, but not as vital as portability.