Problem regarding garbage collection

[rohan yadav]

K&B book page no:259 problem no:2

  class CardBoard{
  Short story = 5;
   CardBoard go (CardBoard cb) {
      cb = null;
      return cb;
   }
 public static void main(String args[]){
 CardBoard c1= new CardBoard();
 CardBoard c2= new CardBoard();
 CardBoard c3= c1.go(c2);
 c1=null;
//do stuff
}}

When //do stuff is reached, how many object are eligible for GC(Garbage collection)?

A. 0
B. 1
C. 2
D. Compilation fails
E. It is not possible to know
F. An Exception is thrown at runtime


Ans: C

I am frustrating by this answer. Can anyone explains me why??
Why doesnt all object are eligible for garbage collection??
Thanks in advance.

[S Ali]

been discussed here