Answer:
The service model employed for the data storage capability of only CST is:
SaaS (Software as a Service).
Explanation:
The three cloud computing categories are Infrastructure as a Service (IaaS), Software as a Service (SaaS), and Platform as a Service (PaaS). The three cloud computing services provide different virtual computing resources. In the case of CST, it utilizes only the data storage software of a provider, who provides the data storage infrastructure, including cloud-based servers, while CST uses its own "laptop and desktop computers and other networking hardware and software to access the Internet efficiently."