Which arrangement of the following lines of code results in an error$-$free program?

$z=y$

$x=3$

$y=x$

A$.$

$z=y$

$x=3$

$y=x$

B$.y=x$

$z=y$

$x=3$

C$.y=x$

$x=3$

$z=y$

D$.x=3$

$y=x$

$z=y$

E$.x=3$

$z=y$

$y=x$