Explanation
Public clouds offer services to anyone, regardless of affiliation, and are the most likely to offer free services to users. Examples of public clouds with free services include iCloud, Dropbox, and OneDrive. Private cloud models are designed for specific customers and for their needs, and would not offer services to the public at large, for free or otherwise. A community cloud is specific to a group of similar organizations and would not offer free or widely available public services. A hybrid cloud model would not fit the specifics of the question.

Explanation/Reference:
Explanation:
Regulatory changes by themselves would not trigger a need for new testing of a BCDR plan. Any changes necessary for regulatory compliance would be accomplished through configuration changes or software updates, which in turn would then trigger the necessary new testing. Annual testing is crucial to any BCDR plan. Also, any time major configuration changes or software updates are done, the plan should be evaluated and tested to ensure it is still valid and complete.

With cloud providers hosting a number of different customers, it would be impractical for them to pursue additional certifications based on the needs of a specific customer. Cloud environments are built to a common denominator to serve the greatest number of customers. Especially within a public cloud model, it is not possible or practical for a cloud provider to alter its services for specific customer demands.
Resource pooling and virtualization within a cloud environment would be the same for all customers, and would not impact certifications that a cloud provider might be willing to pursue.
Regulations would form the basis for certification problems and would be a reason for a cloud provider to pursue specific certifications to meet customer requirements.

Interoperability is ability to easily move between cloud providers, by either moving or reusing components and services. This can pertain to any cloud deployment model, and it gives organizations the ability to constantly evaluate costs and services as well as move their business to another cloud provider as needed or desired. Portability relates to the wholesale moving of services from one cloud provider to another, not necessarily the reuse of components or services for other purposes. Although resiliency is not an official concept within cloud computing, it certainly would be found throughout other topics such as elasticity, auto- scaling, and resource pooling. Scalability pertains to changing resource allocations to a service to meet current demand, either upward or downward in scope.