Which Process Model Activities designate a task completed by the system?

The correct answer is the Script Task because it is specifically designed to perform operations without requiring human intervention. When a Script Task is executed, it runs a predefined set of code or expressions, and the system automatically completes this task as part of the process model, allowing for seamless execution of logic and calculations.

In contrast, a User Task requires input or action from a user, as it is assigned to individuals who must complete the task manually. A Service Task also involves a system operation but is typically used for integrating external services or applications, which still may require some level of user setup. A Sub-process acts as a separate process that can be called from a parent process and may involve various types of tasks, including both user and automated tasks, thereby not strictly designating a task completed solely by the system.