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

public class Car $\{$

private String model;

private int year;

$//$ Constructors and other methods

public void startEngine$()\{$

$//$ Start the car's engine

$\}$

$\}$

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

b$.$ Encapsulate what varies.

c$.$ None

d$.$ Classes are about behavior and functionality.

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