What best describes the prospective modeling elements of a use case diagram?

The prospective modeling elements of a use case diagram are best described by actors, use cases, and associations. In this context, actors represent the roles that interact with the system, such as users or other systems. Use cases refer to the specific functions or processes the system performs in response to the interactions initiated by the actors. Associations illustrate the relationships between the actors and the use cases, showing how actors are connected to the functionalities of the system.

This combination effectively captures the interactions within a system and illustrates how various components work together to fulfill user needs, which is the primary purpose of a use case diagram. In contrast, the other choices either mix elements that don’t typically belong in use case diagrams or lack the essential components that define the actor-use case relationships clearly.