Which statement is true?

Consider the following profile:

Which statement is true?
A . Each instance of Class must be linked to exactly one instance of DisplayArea, Frame, or Form.
B . Each instance of Class must be linked to at most one instance of DisplayArea. Frame, or Form.
C . Each instance of Class must be linked to exactly one instance of DisplayArea. Frame, and Form.
D . Instances of Class or its subclasses do not have to be linked to instances of DisplayArea. Frame, or Form.
E . The diagram is incorrect because a required extension cannot be applied to a stereotype inheritance hierarchy.

Answer: D

Explanation:

The UML diagram fragment provided shows a UML profile with a required extension from the metaclass Class to the stereotype DisplayArea, which in turn has two subclasses Frame and Form. The use of {required} indicates that whenever an instance of Class is extended by the DisplayArea stereotype, it becomes mandatory to do so. However, this does not enforce that every instance of Class must be linked to DisplayArea or its subclasses (Frame or Form). It only means that if the DisplayArea stereotype is applied, it is required. Therefore, there is no obligation for every instance of Class or its subclasses to be stereotyped as DisplayArea, Frame, or Form. It’s also worth noting that the last option (E) could be considered true in some interpretations of UML, but given the options provided and common UML practices, option D is more accurate.