Az alábbi teszt példában miért nem GC-zhető egy nullára állított object?

class A {

private B b;

public A() {

this.b = new B(this);

}

}

class B {

private A a;

public B(A a) {

this.a = a;

}

}

public class Test {

public static void main(String args[]) {

A aa = new A();

aa = null;

// some code goes here

}

}

A) The objects referenced by a and b are eligible for garbage collection.

B) None of these objects are eligible for garbage collection.

C) Only the object referenced by "a" is eligible for garbage collection.

D) Only the object referenced by "b" is eligible for garbage collection.

E) Only the object referenced by "aa" is eligible for garbage collection.

A teszt szerint a helyes válasz az A).

Az E) miért nem jó?