找不到类型或命名空间名称Response（是否缺少 using 指令或程序集引用？)"

我在C#中用了这样语句:Response.Redirect("default.aspx")运行后出现如下错误:
"找不到类型或命名空间名称Response（是否缺少 using 指令或程序集引用？)"
请问各位高手如何写正确的语句?谢谢!!!!!!!!!
我的C#文件(login.cs)源代码如下：
using System;
using System.Collections;
using System.Collections.Specialized;
using System.Data.SqlClient;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
namespace ConsoleApplication1
{
public class Login
{
public TextBox Username;
public HtmlInputText Password;
public HtmlContainerControl ErrorMsg;
public const string ConnectionStrin="server=Twedw; database=Tdw;uid=sa;pwd=";
protected bool authenticate(String user,String pass)
{
bool authenticated = false;
try
{
......
if (((int)IsValid.Value) == 1)
authenticated =true;
}
catch(Exception e)
{
Console.WriteLine("An error occurred: '{0}'", e);
return authenticated;