Which elements are included in a class diagram?

A class diagram is a visual representation of the classes within a system and their relationships. The primary components included in a class diagram are the system's classes, their attributes, and their methods. Classes represent the blueprint of an object, attributes define the properties or characteristics of the objects created from these classes, and methods represent the functions or procedures that the objects can perform.

This choice highlights the structural aspect of object-oriented programming, focusing on the definition and characteristics of classes, which is essential for understanding how data is organized and managed within a software application. This clarity helps developers and designers conceptualize the system and its interrelated components effectively. The other options relate to different aspects of software design, such as interactions, flow control, and user interface, which are not the primary concerns of a class diagram.