DropdownList SelectedIndexChange by jQuery (Cascading)

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
    <script src="Scripts/jquery-1.8.2.js"></script>
    <script type="text/javascript">
        $(function () {
            $('#<%=ddlState.ClientID %>').attr('disabled', 'disabled');
    $('#<%=ddlRegion.ClientID %>').attr('disabled', 'disabled');
    $('#<%=ddlState.ClientID %>').append('<option selected="selected" value="0">Select State</option>');
    $('#<%=ddlRegion.ClientID %>').empty().append('<option selected="selected" value="0">Select Region</option>');
    $('#<%=ddlCountry.ClientID %>').change(function () {
        var country = $('#<%=ddlCountry.ClientID%>').val()
    $('#<%=ddlState.ClientID %>').removeAttr("disabled");
    $('#<%=ddlRegion.ClientID %>').empty().append('<option selected="selected" value="0">Select Region</option>');
    $('#<%=ddlRegion.ClientID %>').attr('disabled', 'disabled');
    $.ajax({
        type: "POST",
        url: "Demo2.aspx/BindStates",
        data: "{'country':'" + country + "'}",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (msg) {
            var j = jQuery.parseJSON(msg.d);
            var options;
            for (var i = 0; i < j.length; i++) {
                options += '<option value="' + j[i].optionValue + '">' + j[i].optionDisplay + '</option>'
            }
            $('#<%=ddlState.ClientID %>').html(options)
},
    error: function (data) {
        alert('Something Went Wrong')
    }
});
});
    $('#<%=ddlState.ClientID %>').change(function () {
        var stateid = $('#<%=ddlState.ClientID%>').val()
    $('#<%=ddlRegion.ClientID %>').removeAttr("disabled");
    $.ajax({
        type: "POST",
        url: "Demo2.aspx/BindRegion",
        data: "{'state':'" + stateid + "'}",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (msg) {
            var j = jQuery.parseJSON(msg.d);
            var options;
            for (var i = 0; i < j.length; i++) {
                options += '<option value="' + j[i].optionValue + '">' + j[i].optionDisplay + '</option>'
            }
            $('#<%=ddlRegion.ClientID %>').html(options)
},
    error: function (data) {
        alert('Something Went Wrong')
    }
});
})
})
</script>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="Maincontent" runat="server">
    <center>
        <table style="width:100%">
            <tr>
                <td colspan="2" class="tdHeader1">
                    Cascade
                </td>
            </tr>
            <tr>
                <td class="label">
                    State :
                </td>
                <td class="labelDescription">
                    <asp:DropDownList ID="ddlCountry" runat="server"></asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="label">
                    District :
                </td>
                <td class="labelDescription">
                    
                    <asp:DropDownList ID="ddlState" runat="server"></asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="label">
                    City :
                </td>
                <td class="labelDescription">
                   <asp:DropDownList ID="ddlRegion" runat="server"></asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="label"></td>
                <td class="labelDescription"></td>
            </tr>
        </table>
    </center>
</asp:Content>

 public partial class Demo2 : System.Web.UI.Page
    {

        //public static string strcon = "Data Source=OTMUMHODTN004/SA;Initial Catalog=INDIACAST;User ID=sa;Password=saadmin@123;Integrated Security=true";
        public static string strcon = ConfigurationManager.ConnectionStrings["Indiacastcms"].ConnectionString;

        #region Page_Load
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindCountries();
            }
        }
        #endregion

        
       #region BindCountries()
        public void BindCountries()
        {
            //String strQuery = "select CountryID,CountryName from MasterCountry";
            //using (SqlConnection con = new SqlConnection(strcon))
            //{
            //    using (SqlCommand cmd = new SqlCommand())
            //    {
            //        cmd.CommandType = CommandType.Text;
            //        cmd.CommandText = strQuery;
            //        cmd.Connection = con;
            //        con.Open();
            //        ddlCountry.DataSource = cmd.ExecuteReader();
            //        ddlCountry.DataTextField = "CountryName";
            //        ddlCountry.DataValueField = "CountryID";
            //        ddlCountry.DataBind();
            //        ddlCountry.Items.Insert(0, new ListItem("<<--Select Country-->>", "0"));
            //        con.Close();
            //    }
            //}
            try
            {
                strSel = "select CountryID,CountryName from MasterCountry";
                ds = common.ExecuteDataSet(strSel,CommandType.Text);

                if(ds.Tables[0].Rows.Count > 0)
                {
                    ddlCountry.DataSource=ds.Tables[0];
                    ddlCountry.DataValueField = "CountryID";
                    ddlCountry.DataTextField = "CountryName";
                    ddlCountry.DataBind();
                    ddlCountry.Items.Insert(0,"<<--Select Country-->>");
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
        #endregion

        #region [WebMethod] BindStates(string country)
        [WebMethod]
        public static string BindStates(string country)
        {
            StringWriter builder = new StringWriter();
            String strQuery = "select StateID,StateName from MasterState where CountryID=@CountryID";
            DataSet ds = new DataSet();
            using (SqlConnection con = new SqlConnection(strcon))
            {
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = strQuery;
                    cmd.Parameters.AddWithValue("@countryid", country);
                    cmd.Connection = con;
                    con.Open();
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    da.Fill(ds);
                    con.Close();
                }
            }
            DataTable dt = ds.Tables[0];
            builder.WriteLine("[");
            if (dt.Rows.Count > 0)
            {
                builder.WriteLine("{\"optionDisplay\":\"<<--Select State-->>\",");
                builder.WriteLine("\"optionValue\":\"0\"},");
                for (int i = 0; i <= dt.Rows.Count - 1; i++)
                {
                    builder.WriteLine("{\"optionDisplay\":\"" + dt.Rows[i]["StateName"] + "\",");
                    builder.WriteLine("\"optionValue\":\"" + dt.Rows[i]["StateID"] + "\"},");
                }
            }
            else
            {
                builder.WriteLine("{\"optionDisplay\":\"--Select State--\",");
                builder.WriteLine("\"optionValue\":\"0\"},");
            }
            string returnjson = builder.ToString().Substring(0, builder.ToString().Length - 3);
            returnjson = returnjson + "]";
            return returnjson.Replace("\r", "").Replace("\n", "");
        }
        #endregion

        #region [WebMethod] BindRegion(string state)
        [WebMethod]
        public static string BindRegion(string state)
        {
            StringWriter builder = new StringWriter();
            String strQuery = "select RegionID, RegionName from MasterRegion where StateID=@StateID";
            DataSet ds = new DataSet();
            using (SqlConnection con = new SqlConnection(strcon))
            {
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = strQuery;
                    cmd.Parameters.AddWithValue("@StateID", state);
                    cmd.Connection = con;
                    con.Open();
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    da.Fill(ds);
                    con.Close();
                }
            }
            DataTable dt = ds.Tables[0];
            builder.WriteLine("[");
            if (dt.Rows.Count > 0)
            {
                builder.WriteLine("{\"optionDisplay\":\"<<--Select Region-->>\",");
                builder.WriteLine("\"optionValue\":\"0\"},");
                for (int i = 0; i <= dt.Rows.Count - 1; i++)
                {
                    builder.WriteLine("{\"optionDisplay\":\"" + dt.Rows[i]["RegionName"] + "\",");
                    builder.WriteLine("\"optionValue\":\"" + dt.Rows[i]["RegionID"] + "\"},");
                }
            }
            else
            {
                builder.WriteLine("{\"optionDisplay\":\"--Select Region--\",");
                builder.WriteLine("\"optionValue\":\"0\"},");
            }
            string returnjson = builder.ToString().Substring(0, builder.ToString().Length - 3);
            returnjson = returnjson + "]";
            return returnjson.Replace("\r", "").Replace("\n", "");
        }
        #endregion
    }
}