Adavnce ComboBox using Ajax dropdownextender

advance combobox that allow to select values from radio
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="dropdownex.aspx.cs" Inherits="dropdownex" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </asp:ToolkitScriptManager>
      
    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    <asp:DropDownExtender ID="TextBox1_DropDownExtender" runat="server"
        DynamicServicePath="" Enabled="True"  DropDownControlID="Panel1" TargetControlID="TextBox1"
        HighlightBackColor="Orange"
            DropArrowBackColor="OrangeRed">
    </asp:DropDownExtender>
    <asp:Label ID="lbl1" runat="server"></asp:Label>
    <asp:Panel
            ID="Panel1"
            runat="server"
            BorderColor="Pink"
            BorderWidth="2"
            >
            <asp:RadioButtonList
                ID="RadioButtonList1"
                runat="server"
                OnSelectedIndexChanged="RadioButtonList1_SelectedIndexChanged"
                AutoPostBack="true"
                >
                <asp:ListItem>Crimson</asp:ListItem>
                <asp:ListItem>Orange</asp:ListItem>
                <asp:ListItem>HotPink</asp:ListItem>
                <asp:ListItem>DarkRed</asp:ListItem>
            </asp:RadioButtonList>
        </asp:Panel>

    
    </form>
</body>
</html>


Thanks