Can an abstract class extend another abstract class?

• A. Yes, but only if it implements all methods
• B. No, abstract classes cannot extend one another
• C. Yes, it can, but it's optional to implement the abstract methods
• D. Yes, but it must be made concrete

Answer: (C)

An abstract class can indeed extend another abstract class, and it is optional for the extending abstract class to implement the abstract methods defined in the parent class. This means that the subclass can inherit the abstract methods from the parent class without being required to provide implementations for them. This design allows for a hierarchy of abstractions, where a subclass can still be declared as abstract itself, giving the flexibility to further define or implement the abstract methods in its own subclasses.

In context, while the parent abstract class can define certain behaviors or properties that its subclasses should adhere to, the subclass has the option to leave those behaviors abstract for further definition down the line. This is particularly useful in large applications where you might want to define shared functionality across multiple layers of subclasses. It promotes a more organized structure where responsibilities can be delegated across various class levels without being overly rigid in immediate implementations.

Other options imply constraints that are not accurate within the context of object-oriented programming principles, which allow this flexibility for abstract classes and their relationships.