how to assign asp.net dropdownlist id and text in jquery using ajax service?

Jquery

<script type="text/javascript">

    $(document).ready(function () {

        getCat();

    });

    function getCat() {

        $.ajax({

            type: "POST",

            url: "Pro.aspx/Select",

            dataType: "json",

            data: {},

            contentType: "application/json; charset=utf-8",

            success: function (data) {

                var jsdata = JSON.parse(data.d);

                $.each(jsdata, function (key, value) {

                    $('#DDLCat').append($

("<option</option>").val(value.id_fk).html(value.Cat));

                });

            },

            error: function (data) {

                alert("Problom on Loading....");

            }

        });

    }

</script>

ASPX Code

<asp:DropDownList ID="DDLCat" class="input-xlarge" runat="server" ClientIDMode="Static" />

C# Code

you can return data to datatable.

     dt = b1.DDL(d1);

   List<Def_SubCat> listcat = new List<Def_SubCat>();

            if (dt.Rows.Count > 0)

            {

                for (int i = 0; i < dt.Rows.Count; i++)

                {

                    Def_SubCat scat = new Def_SubCat();

                    string dctcode = dt.Rows[i]["Cat_code"].ToString();

                    scat.id_fk = Convert.ToInt32(dt.Rows[i]["Category_Id"].ToString());

                    scat.Catecode = dt.Rows[i]["Cat_code"].ToString();

                    scat.Cat = dt.Rows[i]["Category"].ToString() + " [ "+ dctcode + " ] " ;

                    listcat.Insert(i, scat);

                }

            }

            JavaScriptSerializer JSS = new JavaScriptSerializer();

            return JSS.Serialize(listcat);