我正在尝试安装桌面环境，lubuntu但Ubuntu 18.04.02出现以下错误：
$ sudo apt install -y lubuntu-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
lubuntu-desktop : Depends: lubuntu-gtk-core but it is not going to be installed
Depends: lubuntu-gtk-desktop but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
有什么想法可以解决这个问题吗？