Which UML diagrams specifically focus on activities?

Activity diagrams are specifically designed to model the workflow or the various activities in a system. They provide a detailed view of how actions are sequenced and the conditions under which these actions occur, making them ideal for capturing the dynamic aspects of a system's processes. Use Case diagrams, on the other hand, illustrate the functionality of the system from a user's perspective, detailing the interactions between users and the system itself. While Use Case diagrams do not focus on activities in the same way as Activity diagrams, they do provide context for what activities may be performed.

Therefore, the correct choice highlights the relevance of Activity diagrams as the primary representation of activities within UML, while also acknowledging that Use Case diagrams contribute to understanding the context of those activities in relation to user interactions.