asp.net-mvc - ドロップダウンリストを ajax の戻り値で埋める

Question

<script>
    $(document).ready(function () {

        $('#dropdown').change(function () {
            var val = $(this).val();
                $.post("@Url.Action("GetServices","vas")", { catId: $(this).val() }, function (data) {
                    $('#dropdownServices').val(data);// here how to fill dropdownlist with the returned selected item.
                });

        });
    });
</script>

HTML

 @Html.DropDownListFor(x => x.SelectedItem, new SelectList(Model.ListOfServices, "Value", "Text"),"choose an Option");