Java quiz. Which class that implements the interface AA and r

Which class that implements the interface AA and returns the amount of the return value of a() of two given classes is declared correctly:


interface AA {
    int a();
}

class A implements AA {
    public int a() {
        return 1;
    }
}

class B implements AA {
    public int a() {
        return 1;
    }
}


class D implements AA {
    public int a() {
        return new A().a() + new B().a();
    }
}


class D implements AA {
    int a() {
        return new A().a() + new B().a();
    }
}


class D implements AA {
    public int a(A a, B b) {
        return a.a() + new b.a();
    }
}


class D implements AA {
    public int a() {
        return A.a() + B().a();
    }
}

Explanation

Class implementing an interface cannot narrow access modifier, so method a() has to be public.
Number of parameters cannot change with overriding, a(A a, B b) is a different method. But method a() has to be implemented for correct interface implementation.
Method a() is not static and you need an instance of an object to call it, so A.a() will not compile.