Ause case diagramis a visual representation of how users (or systems) interact with a system to achieve specific goals.Actorsrepresent the entities (e.g., users or external systems) that expect to receive services from the system.

Key Elements of a Use Case Diagram:

Actors:Represent individuals or systems that interact with the system to achieve a goal.

System Boundaries:Define the scope of the system being modeled.

Users:While "users" may seem similar to actors, the term "actors" is the correct technical term in use case diagrams.

Entities:Entities typically refer to data objects or components, not those receiving services.

Evaluation of Each Option:

A. Actors:Actors are the correct element used to indicate those who expect to receive a service from the system.Conclusion:This iscorrect.

B. System boundaries:System boundaries define the scope of the system but do not represent those receiving services.Conclusion:This isnot correct.

C. Users:While users may interact with the system, the correct term in use case diagrams is "actors."Conclusion:This isnot correct.

D. Entities:Entities represent data objects or components, not those receiving services.Conclusion:This isnot correct.