Messsage doesn't show

[pt0909]

I need to show a message whenever user Select option"A"
heres the code for aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="~/Search.aspx.cs" Inherits="HITS.Search" MasterPageFile="~/hits_main.master"%>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <asp:ScriptManager ID="scMgr" runat="server"/>
<div>
<%--<asp:UpdatePanel ID="UP1" runat="server" >
  <ContentTemplate> 
  </ContentTemplate>
 
</asp:UpdatePanel> --%>
    <table  cellspacing="10" border=".02">   
    <tr>   
      <td   align="left"  > 
          <asp:RadioButtonList ID="RBl1" runat="server" AutoPostBack="True"                               
                                CellPadding="2" CellSpacing="5" 
              onselectedindexchanged="RBl1_SelectedIndexChanged">
            <asp:ListItem  Value="G" Selected="True" >Regular Grants</asp:ListItem>
            <asp:ListItem Value ="A">ARRA Grants</asp:ListItem>
            <asp:ListItem Value ="C">Contract</asp:ListItem>
            </asp:RadioButtonList>                 
         
         </td>