Question: What is an abstract class?

1. An abstract class is the name for any class from which you can instantiate an object.
2. Abstract classes must be redefined any time an object is instantiated from them.
3. Abstract classes must inherit from concrete classes.
4. An abstract class exists only so that other "concrete" classes can inherit from the abstract class.

Answer: The correct answer of the above question is Option D:An abstract class exists only so that other "concrete" classes can inherit from the abstract class.