Thank you very much for your kindly reply. I install these desktop environment in ubuntu bionic. A dialog box pops up when I install gnome, let me choose which desktop environment to use. I choose gdm3 and reboot. After reboot, there are some errors in TTY, and cursor keeps flashing. If I press ctrl+alt+F4, I can see TTY let me to login. I can't see any dialog box list of available desktop environment. I'm sorry, I have reinstalled the system, so I can't show you the errors.