procedure TForm1.ComboBox1Change(Sender: TObject);
begin
if combobox1.itemindex = 0
then Form2.Show;
begin
Form3.Hide; Form4.Hide
end;
if combobox1.itemindex = 1
then Form3.Show;
begin
Form2.Hide; Form4.Hide;
end;
if combobox1.itemindex = 2
then Form4.Show;
begin
Form2.Hide; Form3.Hide;
    end;
  end;
end.