Drop Down List Repeatedly populate the Existing Data

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ASP.NET4

Dear Friend


i have a problem using dropdownlist. however code is working but there is a problem when i select an item from the drop down list and the gridview show the result accordingly but dropdownlist repeats its existing data again and again.

Here is a code plz please rectify it

protected void Page_Load(object sender, EventArgs e)
        {
            string cs = ConfigurationManager.ConnectionStrings["LibraryDatabase"].ToString();
            using (SqlConnection con = new SqlConnection(cs))
            {
                SqlCommand cmd = new SqlCommand("select * from tblBooks  where Title=@TITLE", con);
                cmd.Parameters.AddWithValue("@TITLE", DropDownList1.SelectedValue);
                SqlCommand cmd1 = new SqlCommand("select Title from tblBooks",con);
                
                con.Open();
                SqlDataReader rdr = cmd.ExecuteReader();
                GridView1.DataSource = rdr;
                GridView1.DataBind();
                rdr.Close();
                SqlDataReader rdr1 = cmd1.ExecuteReader();

                while (rdr1.Read() == true)
                {
                    DropDownList1.Items.Add(new ListItem( rdr1["Title"].ToString()));
               }

                rdr1.Close();
            }
        }