private void caudung_Click(object sender, EventArgs e)
        {
            btnNha2 nha2 = new btnNha2();

            nha2.Show();
            this.Close();
        }
        private void button10_Click(object sender, EventArgs e)
        {
            btnNha2 lv2 = new btnNha2();

            lv2.Show();
            this.Close();
        }