Final answer:
An event list identifies external events that could trigger behavior in a system and defines the scope boundary for the system.
Step-by-step explanation:
The correct answer to the question is D. An event list. An event list identifies external events that could trigger behavior in a system. It includes possible business events initiated by users, as well as time-triggered (temporal) events or signal events from external components such as hardware devices. This list is crucial in defining the scope boundary for a system and aids in understanding how the system interacts with its environment. The event list essentially describes what can happen and when it can happen, which is instrumental in the planning phase of system development.