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mock problem

 
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10. abstract class A {
11. abstract void a1();
12. void a2() { }
13. }
14. class B extends A {
15. void a1() { }
16. void a2() { }
17. }
18. class C extends B { void c1() { } }
and:
A x = new B(); C y = new C(); A z = new C();
What are four valid examples of polymorphic method calls? (Choose four.)
options are

A. x.a2();
B. z.a2();
C. z.c1();
D. z.a1();
E. y.c1();
F. x.a1();

My ans is (A,B,E,F)
but correct ans is(A,B,D,F) how?
why e is not valid ans?
 
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for Polymorphism
parent_class var = new child_class();
In c y = new c();
thereis no polymorphism
 
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E is not correct because, y is an object of class C and c1() method is also of class C. So y is calling its own method which is a normal behavior and no polymorphism is involved...
 
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