Identify the object$-$oriented principle applied in this code.

public interface Shape $\{$

double calculateArea$()$;

$\}$

public class Circle implements Shape $\{$

private double radius;

$//$ Constructor and other methods

@Override

public double calculateArea$()\{$

return Math. $\frac{?}{PI}*$ radius $*$ radius;

$\}$

$\}$

a$.$ Each class in your application should have only one reason to change.

b$.$ None

c$.$ Encapsulate what varies.

d$.$ Classes are about behavior and functionality.

e$.$ Code to an interface rather than to an implementation.