Representational State Transfer (REST) is a software architectural scheme that applies the components, connectors, and data conduits for many web applications used on the Internet. It uses and relies on the HTTP protocol and supports a variety of data formats.

SOC 2 deals with the CIA triad. SOC 1 is for financial reporting. SOC 3 is only an attestation by the auditor.
There is no SOC 4.

Explanation
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.

Adopted in 1995, Directive 95/46 EC establishes strong data protection and policy requirements, including the declaring of data privacy to be a human right. It establishes that an individual has the right to be notified when their personal data is being access or processed, that it only will ever be accessed for legitimate purposes, and that data will only be accessed to the exact extent it needs to be for the particular process or request.

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.