Invalid attempt to call HasRows when reader is closed.

String qr = "select * from stusub where StuID='" + gv1.SelectedRow.Cells[1].Text + "' ";
        SqlCommand cm = new SqlCommand(qr, conn);
        conn.Open();
        SqlDataReader dr1 = cm.ExecuteReader();

        DataTable dt1 = new DataTable();
       
        dt1.Load(dr1);

        for (int i = 0; i < dt1.Rows.Count; i++)
        {
            foreach (ListItem item in lbSubject.Items)
            {
                if(dr1.HasRows)
                {
                    item.Selected = true;
                    lbSubject.SelectedValue = Convert.ToString(dt1.Rows[i]["SubID"]);
                }
            }
        }
        conn.Close();