If your application computing architecture involves $2($two$)$ clients for the user interface, $2$ application servers for business logic and $1$ database server, it is an example of $\_\_\_\_\_\_\_\_\_\_$ computing architecture.

$1.$

$5($five$-$tier$)$ client$/$server

$2.$

$2($two$-$tier$)$ client$/$server

$3.$

$3($three$-$tier$)$ client$/$server

$4.$

n$-$tier client$/$server