Answer: (i) Method overriding

Runtime polymorphism occurs when a superclass reference refers to a subclass object and an overridden instance method is selected according to the object's actual type at runtime.

class Animal { void sound() { System.out.println("sound"); } }
class Dog extends Animal { @Override void sound() { System.out.println("bark"); } }
Animal a = new Dog();
a.sound(); // bark