Exam 1z0-851 topic 1 question 39 discussion

Actual exam question from Oracle's 1z0-851

Question #: 39
Topic #: 1

Given:
10. interface Foo {}
11. class Alpha implements Foo {}
12. class Beta extends Alpha {}
13. class Delta extends Beta {
14. public static void main( String[] args ) {
15. Beta x = new Beta();
16. //insert code here
17. }
18. }
Which code, inserted at line 16, will cause a java.lang.ClassCastException?