Head First Garbage collector exercise

//which of the lines of code on the right, if added to the class on the left at point A,
//would cause eactly one additional object to be eligible
public class GC {
  public static GC dostuff();
     GC newGC = new GC();
     doStuff2(newGC);
     return newGC;
  }

public static void main(String [] args) {
  GC gc1;
  GC gc2 = new GC();
  GC gc3 = new GC();
  GC gc4 = gc3;
  gc1 = doStuff();

  // call more methods

gc2 = null;
gc1 = null;
gc1 = gc4;
}

public static void doStuff2(GC copy GC) {
  GC localGC
 }
}