using ExtensionMethods; asp.net 4.0 报错

[xiaotuzi]

using System;
using System.Collections;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using ExtensionMethods;
public partial class _3_8 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
List<C31> New_t = new List<C31>();
New_t.Add(new C31("陈同学", new DateTime(1988, 10, 3), "454521198810030023"));
New_t.Add(new C31("李同学", new DateTime(1978, 4, 3), "454521197804030023"));
int i = 1;
foreach (var p in New_t)
{
Response.Write("**********第" + i.ToString() + "名学生***********" + "<br/>");
Response.Write("姓名：" + p.st_name + "<br/>");
Response.Write("出生日期：" + p.st_csrq.ToString("yyyy-MM-dd") + "<br/>");
Response.Write("身份证：" + p.st_code + "<br/>");
Response.Write("入学年龄：" + p.st_rsnl.ToString() + "<br/>");
i += 1;
}



}
}

以上是源代码

出错信息为

错误 1 未能找到类型或命名空间名称“ExtensionMethods”(是否缺少 using 指令或程序集引用?) D:\devtools\源代码\第3章\c3\3-8.aspx.cs 14

[熊猫无敌]

直接去掉看看？