Interview question: Objects eligible for garbage collection

Give the following code:

class A {
    Boolean b;
    A easyMethod(A a){
        a = null;
        return a;
    }
    public static void main(String [] args){
        A a1 = new A();
        A a2 = new A();
        A a3 = new A();
        a3 = a1.easyMethod(a2);
        a1 = null;
        // Some other code 
    }
}

The question is how many objects are eligible for garbage collection right before // Some other code.

Then correct answer is (at least that's the interviewer answer): 2 - the Boolean b because it's a wrapper and a1 .

Can you please me explain me why a2 and a3 aren't being garbage collected ?

LATER EDIT:

• Ok, I think I get it now. It was a bit confusing at first, but now i am sure the interviewer was wrong. My initial mistake was that at first I didn't consider that Java is pass by value only, so it's impossible to make a2 null from inside a function that take "a2" as a parameter, because that a2 is actually a copy of a2.
• The part with the Boolean b was indeed quite obvious.

Thanks for an answer, I will send some interview feedback after that :).