How to use response.redirect without changing current URL

 In my left panel have some menus  , once if u click that menu then it would pass some values to master page ......remaining under here
 Site.Master
<%@ master language="VB" %>
<%@ import Namespace="system.IO" %>
<%@ import Namespace="system.Net" %>
<%@ Register TagPrefix="leftMenu" TagName="leftMenuIndex" src="./includes/leftpanel.ascx" %>
<script runat="server">
    Sub page_load()
      
        If (IsNothing(Request.QueryString("c"))) Then
            Response.Write("<h2>File Not Found</h2>")
        Else
            If (File.Exists(Serv ...