将PHP查询到Mysql数据库

I have this query to a database, the problem is that the query works only when it receives the code AFG , with any other countrycode (example DEL) returns nothing. I haven't got conection error , using AFG code WORK but with any other that exists no

the database scheme is world -> city -> id , Name , CountryCode , District , Population

<?php

$host = "localhost";
$user = "root";
$pass = "";
$db   = "world";


$respuesta = [];

$selec  = $_GET["selected"];

$ms = mysqli_connect($host, $user, $pass);
    if (!$ms){
        $mensaje = 'ERROR: No pude conectar al servidor MySQL';
    }else{
        if (mysqli_select_db($ms, $db)){


            $q = "SELECT * FROM  `city` WHERE `CountryCode`='".$selec."'";

            $r = mysqli_query($ms, $q); 


            while($row = mysqli_fetch_assoc($r)){
                $cadena = '<option value="'.$row["ID"].'">'.$row["Name"].'</option>';
                array_push($respuesta,$cadena);


            }

        }



    }


    echo json_encode($respuesta);
    ?>