private void richTextBox1_KeyDown(object sender, KeyEventArgs e)

        {

            if (e.Control && e.KeyCode == Keys.C)

            {

                e.Handled = true;

                MessageBox.Show("Ctrl+C组合键已经被屏蔽","温馨提示");

            }

            if (e.Control && e.KeyCode == Keys.V)

            {

                e.Handled = true;

                MessageBox.Show("Ctrl+V组合键已经被屏蔽", "温馨提示");

            }

            if (e.Control && e.KeyCode == Keys.X)

            {

                e.Handled = true;

                MessageBox.Show("Ctrl+X组合键已经被屏蔽", "温馨提示");

            }

        }