显示的错误是““GridView3”上同时定义了 DataSource 和 DataSourceID。请移除一个定义。”

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace 志愿通
{
public partial class 历史类 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

    }

    protected void 查询_Click(object sender, EventArgs e)

    {
        String ConnStr = "Data Source=DESKTOP-3IT6TKJ;Initial Catalog=成绩表;Integrated Security=True";
        SqlConnection conn = new SqlConnection(ConnStr);

        SqlCommand cmd = new SqlCommand();
        cmd.Connection = conn;
        cmd.CommandText = "SELECT 累计人数 FROM 一分一段历史表 WHERE 分数 = '" + 输入分数.Text.Trim() + "'";
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader();

        this.GridView3.DataSource = dr;
        this.GridView3.DataBind();

有在别的地方赋值了GridView3.DataSourceID吗