Mark works as a Programmer for InfoTech Inc. He creates a program that uses the following code.

1. class Book

2. {

3. Short f1= 15;

4. Book GetDetails(Book b1)

5. {

6. b1=null;

7. return b1;

8. }

9. public static void main(String args[])

10. {

11. Book b1 = new Book();

12. Book b2 = new Book();

13. Book b3 = b1.GetDetails(b2);

14. b1=null;

15. //code

16. }

17. }

How many objects will be eligible for garbage collection when line 15 is reached?