Page 844 - AP Computer Science A, 7th edition

8. (D) The withdraw method is the only method that has one implementation in the superclass and a different implementation in a subclass. Polymorphism is the mechanism of selecting the correct method from the different possibilities in the class hierarchy. Notice that the deposit method, for example, is available to objects of all three bank account classes, but it’s the same code in all three cases. So polymorphism isn’t tested.