What language features of C# are used to implement polymorphism?

In C#, polymorphism is implemented using keywords and mechanisms that allow methods and properties to behave differently depending on the object's type at runtime. The main tools are:

• virtual — declares a method or property that can be overridden in a derived class.
• override — used in a derived class to override a virtual method of the base class.
• abstract — declares an abstract method or class that must be implemented in subclasses.
• interface — defines a contract that different classes can implement, providing polymorphic behavior.

Example:

public abstract class Animal
{
    public abstract void Speak();
}

public class Dog : Animal
{
    public override void Speak() => Console.WriteLine("Woof");
}

public class Cat : Animal
{
    public override void Speak() => Console.WriteLine("Meow");
}

// Usage
Animal a = new Dog();
 a.Speak(); // Outputs "Woof"

a = new Cat();
 a.Speak(); // Outputs "Meow"

Thus, polymorphism allows working with objects through the base type, calling overridden methods of specific classes.