To answer this question, you need to understand the concepts of "has-a" and "is-a" relationships.
Option A) Inheritance represents an is-a relationship - This option is correct. Inheritance is a mechanism in object-oriented programming that allows a class to inherit properties and behaviors from another class. An is-a relationship represents a relationship where one class is a specialized version of another class. For example, if we have a class called "Animal" and another class called "Cat", the "Cat" class can inherit from the "Animal" class because a cat is a type of animal.
Option B) Inheritance represents a has-a relationship - This option is incorrect. Inheritance represents an is-a relationship, not a has-a relationship. A has-a relationship is a composition relationship where one class contains an instance of another class as a member variable. For example, if we have a class called "Car" and another class called "Engine", the "Car" class can have an instance variable of type "Engine" to represent that a car has an engine.
Option C) Interfaces must be used when creating a has-a relationship - This option is incorrect. Interfaces are not required when creating a has-a relationship. Interfaces are used to define a contract that classes must implement, but they are not necessary for creating a has-a relationship. Has-a relationships can be created using instance variables without the need for interfaces.
Option D) Instance variables can be used when creating a has-a relationship - This option is correct. Instance variables can be used to create a has-a relationship between classes. By declaring an instance variable of one class inside another class, we can represent that the class has a relationship with the other class.
Therefore, the correct answers are A) Inheritance represents an is-a relationship and D) Instance variables can be used when creating a has-a relationship.