I think my code has problem

public class Mean
        {
            static public string nghia;

        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            string a = null, text = null;
            a = Clipboard.GetText();
            text = a.ToLower();
            for (int i = 0; i < cbbtu.Items.Count; i++)
            {
                if (cbbtu.Items[i].ToString() == text)
                {
                    cbbtu.SelectedIndex = i;
                    Form clipbr = new clp();
                    clipbr.Show();
                }
            }
        }