刚刚学习c#，请问如何判定选择

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Count_Main.aspx.cs" Inherits="functions_Count_Main" %>
<%@ Register TagPrefix="iewc" Namespace="Microsoft.Web.UI.WebControls" Assembly="Microsoft.Web.UI.WebControls" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title></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">
<link rel="stylesheet" type="text/css" href="/emay.css">
<script language="javascript" for="Toolbar1" event="onbuttonclick">
switch (event.srcNode.getAttribute('ID'))
{
case 'refresh':
location = 'ServerManageEmailQueue.aspx';
break;
}
</script>
<script language="javascript">
function HoverHeader(obj, on)
{
if (on)
obj.style.borderTop='orange 1px solid';
else
obj.style.borderTop='white 1px solid';
}

function Sort(colName)
{
}

function StatusChanged(id)
{
var command = document.all['cmb' + id].item(document.all['cmb' + id].selectedIndex).value;
location = 'EmailQueueManage.aspx?QueueID=' + id + '&Command=' + command;
}

// 上次选中的ID
var selID = '';
function SelectRecord(id)
{
if (selID != '')
{
document.all['TR' + selID].style.backgroundColor = '';
document.all['TR' + selID].style.color = '';
}

selID = id;
document.all['TR' + id].style.backgroundColor = 'gold';
document.all['TR' + selID].style.color = 'black';
}

function HoverRecord(id, focus)
{
if (typeof(document.all['TR' + id]) != 'undefined')
{
if (focus)
{
document.all['TR' + id].bgColor = 'PaleGoldenrod';
}
else
{
document.all['TR' + id].bgColor = '';
}
}

}
function Check()
{
    var check_value = "";
    var two_check_value = "";
   var   a   =   document.getElementsByName("rd_check");   
                for   (var   i=0;   i<a.length;   i++)   
                {   
                        if(a[i].checked){   
                         check_value=a[i].value;
                         }   
                }   
              
               var   aa   =   document.getElementsByTagName("rd_check_history");   
               two_check_value =document.all['rd_check_history'].checked;
               if(check_value=="重复次数")
               {
                 alert("按照'"+check_value+"'统计")
                 window.parent.frames['countframe'].location = '/functions/Count_ChongFu.aspx?history='+two_check_value
               }
               if(check_value=="归属地")
               {
                    alert("按照'"+check_value+"'统计")
                    window.parent.frames['countframe'].location = '/functions/Count_GuiShuDi.aspx?history='+two_check_value
               }     
}
</script>
</HEAD>
<body MS_POSITIONING="GridLayout">
<form id="Form1" method="post" runat="server">
<table border="0" height="100%" width="100%" cellpadding="0" cellspacing="0">

<tr>
<td colspan="3" height="100%">
<!--邮件统计表-->
<div style="OVERFLOW: auto; HEIGHT: 100%">
    
<table border="0" width="100%" align="center" bgcolor="white" cellspacing="0" cellpadding="2">
<tr>
    <td><asp:Panel ID="Panel1" runat="server" Height="50px" Width="125px" BorderStyle="Inset">
                                     <input id="rd_check" name="rd_check" type="radio" checked value="重复次数">重复次数<br />
                                     <input id="Radio1"  name="rd_check" type="radio" value="归属地">归属地
                                     </asp:Panel>
    </td>
</tr>
<tr>
    <td> 
    </td>
</tr>
<tr>
    <td> 
                                    <input type=checkbox name="rd_check_history" id="rd_check_history" value="历史对比">同时进行历史对比
    </td>
</tr>
<tr><td>
<input type=button value="统计" onclick="javascript:Check()" />
</td></tr>
 </table>

</div>

</td>
</tr>
</table>
</form>
</body>
</HTML>
如何选择重复次数的时候不显示历史对比，只有在选择了历史对比的时候才出现历史对比，归属地也一样