Class D is a superclass of Class A. It sits at a higher level in the inheritance hierarchy and passes down properties and methods to Class A.
Superclass/Subclass: Just like any other superclass-subclass relationship, there will be an inheritance connection between Classes D and A.
Inheritance allows properties and behaviors defined in the superclass (Class D) to be passed down to its subclasses (like Class A).
Polymorphism enables objects of different subclasses (including Class A) to be treated as objects of their shared superclass.