Inheritance and Method Calls

Consider the following class definitions.

public class ClassA {
    public void methodA() {
        /* implementation not shown */
    }

    // Other methods are not shown.
}

public class ClassB extends ClassA {
    public void methodB() {
        /* implementation not shown */
    }

    // Other methods are not shown.
}

In a client class, the following declarations are made. Assume that ClassA and ClassB each have a no-argument constructor.

ClassA c1 = new ClassA();
ClassA c2 = new ClassB();

Which of the following method calls will result in a compile-time error?

I. c1.methodB();
II. c2.methodB();
III. c2.methodA();