请教大家一个小问题
我是ASP.NET的初学者,我按照书上的例子试做一个程序,,,功能是选择不同的单选按钮显示不同的图片,,,可是不知道是哪里出了问题,,,选择按钮后图片不发生变化,请大家帮忙看看,,,下面是代码 
 using   System; 
 using   System.Collections; 
 using   System.ComponentModel; 
 using   System.Data; 
 using   System.Drawing; 
 using   System.Web; 
 using   System.Web.SessionState; 
 using   System.Web.UI; 
 using   System.Web.UI.WebControls; 
 using   System.Web.UI.HtmlControls;   
 namespace   Webxx2 
 { 
 	///    <summary>  
 	///   WebForm1   的摘要说明。 
 	///    </summary>  
 	public   class   WebForm1   :   System.Web.UI.Page 
 	{ 
 		protected   System.Web.UI.WebControls.RadioButtonList   RadioButtonList1; 
 		protected   System.Web.UI.WebControls.Image   Image1;  	 
 		private   void   Page_Load(object   sender,   System.EventArgs   e) 
 		{ 
 			//   在此处放置用户代码以初始化页面 
 			Image1.ImageUrl=RadioButtonList1.Items[0].Value;   
 		}   
 		#region   Web   窗体设计器生成的代码 
 		override   protected   void   OnInit(EventArgs   e) 
 		{ 
 			// 
 			//   CODEGEN:   该调用是   ASP.NET   Web   窗体设计器所必需的。 
 			// 
 			InitializeComponent(); 
 			base.OnInit(e); 
 		}  		 
 		///    <summary>  
 		///   设计器支持所需的方法   -   不要使用代码编辑器修改 
 		///   此方法的内容。 
 		///    </summary>  
 		private   void   InitializeComponent() 
 		{             
 			this.RadioButtonList1.SelectedIndexChanged   +=   new   System.EventHandler(this.RadioButtonList1_SelectedIndexChanged); 
 			this.Load   +=   new   System.EventHandler(this.Page_Load);   
 		} 
 		#endregion   
 		private   void   RadioButtonList1_SelectedIndexChanged(object   sender,   System.EventArgs   e) 
 		{ 
 			Image1.ImageUrl=RadioButtonList1.SelectedItem.Value;  		 
 		} 
 	} 
 }   
 还有HTML代码 
  <%@   Page   language= "c# "   Codebehind= "WebForm1.aspx.cs "   AutoEventWireup= "false "   Inherits= "Webxx2.WebForm1 "   %>  
  <!DOCTYPE   HTML   PUBLIC    "-//W3C//DTD   HTML   4.0   Transitional//EN "   >  
  <HTML>  
 	 <HEAD>  
 		 <title> WebForm1 </title>  
 		 <meta   name= "GENERATOR "   Content= "Microsoft   Visual   Studio   .NET   7.1 ">  
 		 <meta   name= "CODE_LANGUAGE "   Content= "C# ">  
 		 <meta   name= "vs_defaultClientScript "   content= "JavaScript ">  
 		 <meta   name= "vs_targetSchema "   content= "http://schemas.microsoft.com/intellisense/ie5 ">  
 	 </HEAD>  
 	 <body   MS_POSITIONING= "GridLayout ">  
 		 <form   id= "Form1 "   method= "post "   runat= "server ">  
 			 <asp:RadioButtonList   id= "RadioButtonList1 "   style= "Z-INDEX:   101;   LEFT:   112px;   POSITION:   absolute;   TOP:   104px " 
 				runat= "server ">  
 				 <asp:ListItem   Value= "add.jpg "   Selected= "True "> image1 </asp:ListItem>  
 				 <asp:ListItem   Value= "BaseItemInout.jpg "> image2 </asp:ListItem>  
 				 <asp:ListItem   Value=