申論題

10. interface A{void x()；} 

11. class B implements A{public void x(){} public void y(){}}

 12. class C extends B{public void x(){}} 

And: 

20. java.util.List＜A＞ list = new java.util.ArrayList＜A＞()；

 21. list.add(new B())； 

22. list.add(new C())； 

23. for(A a : list){ 

24. a.x()；

 25. a.y()； 

26. } 

What is the result? (A) The code runs with no output. (B) An exception is thrown at runtime. (C) Compilation fails because of an error in line 20. (D) Compilation fails because of an error in line 21. (E) Compilation fails because of an error in line 23. (F) Compilation fails because of an error in line 25.