Cascading Dropdownlist using webservices

Here is Html
 <form id="form1" runat="server">

    <asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">

    </asp:ToolkitScriptManager>

    <div>

        <table style="width: 100%;">

            <tr>

                <td colspan="3" class="style2">

                    <h1 align="center">

                        Cascading Dropdown List Style

                    </h1>

                </td>

            </tr>

            <tr>

                <td class="style1">

                    Selecte Country&nbsp;:-

                </td>

                <td>

                    <asp:DropDownList ID="DropDownList1" runat="server">

                    </asp:DropDownList>

                    <asp:CascadingDropDown ID="CascadingDropDown4" runat="server" TargetControlID="DropDownList1"

                        LoadingText="Loding Country" Category="Country" PromptText="Selecte Country"

                        ServiceMethod="Getcountry" ServicePath="~/WebService.asmx">

                    </asp:CascadingDropDown>

                </td>

                <td>

                </td>

            </tr>

            <tr>

                <td class="style1">

                    Selecte State:-

                </td>

                <td>

                    <asp:DropDownList ID="DropDownList2" runat="server">

                    </asp:DropDownList>

                    <asp:CascadingDropDown ID="CascadingDropDown2" runat="server" TargetControlID="DropDownList2"

                        ParentControlID="DropDownList1" Category="State" LoadingText="Loading State"

                        PromptText="Selecte State" ServiceMethod="Getstate" ServicePath="~/WebService.asmx">

                    </asp:CascadingDropDown>

                </td>

                <td>

                    &nbsp;

                </td>

            </tr>

            <tr>

                <td class="style1">

                    Selecte City:-

                </td>

                <td>

                    <asp:DropDownList ID="DropDownList3" runat="server">

                    </asp:DropDownList>

                    <asp:CascadingDropDown ID="CascadingDropDown3" runat="server" TargetControlID="DropDownList3"

                        ParentControlID="DropDownList2" PromptText="Selecte City" Category="City" LoadingText="Loading City"

                        ServiceMethod="Getcity" ServicePath="~/WebService.asmx">

                    </asp:CascadingDropDown>

                </td>

                <td>

                    &nbsp;

                </td>

            </tr>

        </table>

    </div>

    </form>

WebService.cs  below code

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.Services;

using System.Data;

using System.Data.SqlClient;

using AjaxControlToolkit;

using System.Collections.Specialized;

/// <summary>

/// Summary description for WebService

/// </summary>

[WebService(Namespace = "http://tempuri.org/")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.

[System.Web.Script.Services.ScriptService]

public class WebService : System.Web.Services.WebService

{

    public WebService()

    {

        //Uncomment the following line if using designed components

        //InitializeComponent();

    }

    [WebMethod]

    public string HelloWorld()

    {

        return "Hello World";

    }

    [WebMethod]

    public static CascadingDropDownNameValue[] Getcountry(string knownCatagoryValues, string catagory)

    {

        String str1 = "Select * from country_master";

        DataTable dt = new DataTable();

        bal b = new bal();

        dt = b.bind(str1);

        List<CascadingDropDownNameValue> oq = new List<CascadingDropDownNameValue>();

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

        {

            oq.Add(new CascadingDropDownNameValue(dt.Rows[i]["country_name"].ToString(), dt.Rows[i]["country_id"].ToString()));

        }

        return oq.ToArray();

    }

    [System.Web.Services.WebMethod]

    public static CascadingDropDownNameValue[] Getstate(string knownCatagoryValues, string catagory)

    {

        StringDictionary countrydetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCatagoryValues);

        int counrtid = Convert.ToInt32(countrydetails["Country"]);

        String str2 = "Select * from state_master where country_id =" + counrtid + "";

        DataTable ddt = new DataTable();

        bal b = new bal();

        ddt = b.bind(str2);

        List<CascadingDropDownNameValue> st = new List<CascadingDropDownNameValue>();

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

        {

            st.Add(new CascadingDropDownNameValue(ddt.Rows[i]["state_name"].ToString(), ddt.Rows[i]["country_id"].ToString()));

        }

        return st.ToArray();

    }

    [System.Web.Services.WebMethod]

    public static CascadingDropDownNameValue[] Getcity(string knownCatagoryValues, string catagory)

    {

        StringDictionary countrydetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCatagoryValues);

        int Sid = Convert.ToInt32(countrydetails["State"]);

        String str3 = "Select * from city_master where state_id=" + Sid + "";

        DataTable zdt = new DataTable();

        bal b = new bal();

        zdt = b.bind(str3);

        List<CascadingDropDownNameValue> ct = new List<CascadingDropDownNameValue>();

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

        {

            ct.Add(new CascadingDropDownNameValue(zdt.Rows[i]["city_name"].ToString(), zdt.Rows[i]["state_id"].ToString()));

        }

        return ct.ToArray();

    }

}