问Jquery -获取其他下拉列表的值

EN

$('#collo').change(function(){
    $('#collos_gewicht').empty();
    var value = $("#collo").val();
    var vervoerder $('#vervoerder_id').val();
    var dataString = 'value=' + value + '&vervoerder=' + vervoerder;
    $.ajax({
        url: "collos_gewicht.php",
        data: dataString,
        dataType:"html",
        type: "post",
        success: function(data){
           $('#collos_gewicht').append(data);
        }
    });
});

<select name="vervoerder_id">
<option value="1">PostNL</option>
<option value="2">PostNL Pickup Locatie</option>
<option value="3">UPS</option>
<option value="5">TNT Pallet</option>
<option value="6">Zelf afhalen</option>
</select>

<select name="collo" id="collo">
<option value="">Choose the number of collos</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
</select>