Which of the following environments utilizes a subset of customer data and is most likely...

A staging environment is a controlled setting that closely mirrors the production environment but uses a subset of customer data. It is used to test major system upgrades, assess their impact, and demonstrate new features before they are rolled out to the live production environment. This ensures that any issues can be identified and addressed in a safe environment before affecting end-users.

References = CompTIA Security+ SY0-701 study materials, particularly in the domain of secure system development and testing environments​​.